Steve uses the term "Ethical Subjectivism", but I think this term is misleading. Ethical Subjectivism is often used to label the view that subjective belief makes objective ethical statements true: If Hitler believes that killing Jews is right, then killing Jews is right. The views that Steve is apparently critiquing are better labeled as meta-ethical relativism (MESR), which is a position on ethical statements, not a position on ethics.
Two technical points about ethical subjectivsm: (1) the relativity of moral rightness - on this view, there is no sense of moral rightness apart from what someone believes; (2) the personal infallibility of moral judgment – it is impossible on this view for anyone to be wrong when they make a moral claim because rightness for them is just what they think it is.Aside from the misleading connotation of "infallible", this is a pretty good description of MESR.
But the use of "infallible" in (2) deserves special mention. "Infallible" connotes being trustworthy or veridical. The Pope, for instance, is infallible (speaking ex cathedra) not only about his own opinion, but about objective truths concerning God. Steve's use of the word subtly connotes not just that individuals have privileged access to their own mental states, but that the content of these states is veridical. Such a connotation flatly contradicts (1).
Naturally, a charitable reading of Steve's remarks clearly indicates that any speaker is "infallible" in the looser sense that he knows his own states. Still, given what I see as the massive confusion in philosophical discourse between ethical subjectivism and meta-ethical subjective relativism, even an uncharitable connotation deserves specific mention because it subtly suggests an incorrect view to the reader.
Steve later gives us a sensible interpretation, but he first criticizes the supposed subjectivist view of tolerance:
When I teach ethics, the most common view in the room is Ethical Subjectivism, that moral judgments are purely a matter of personal decision. Everyone has his or her own ethical system and the fact that you consider an act morally right means that, for you, the act is morally right. [abrupt segue] While it comes from a good place, the desire to be tolerant, it is in fact, fatally flawed. Turning tolerance from a virtue into the only virtue undermines all meaningful ethical deliberation and handcuffs those who really think tolerance is important.Notice the abrupt segue: Reading Steve's essay, you might think that (meta-)ethical subjectivism entails that tolerance is the only virtue. Steve gives us no argument whatsoever for this conclusion. It's not only a non sequitur, but it's also a logical contradiction.
Consider the statement:
(T) It is always good to be tolerant(T) is an objective ethical statement: It does not, directly or indirectly reference any statement of mind, and it makes a specific assertion about what is good. However, meta-ethical subjective relativism specifically denies that any such objective statement can have a truth value.
The only way to get to (T) is to reintroduce ethical objectivism through the "back door" with the enthymeme:
P1: only statements that are objectively true are ethically relevantBut P1 not only flatly contradicts MESR, it is also--by virtue of being expressed objectively--contrary to the spirit of MESR.
Subjectivism and Taste
Steve correctly notes that under MESR, "reasoning about ethics now becomes akin to choosing a favorite flavor of ice cream." Akin to is the key phrase: there is a point of similarity, but not of identity. Therefore the observation that
That horrible knot in the pit of your stomach wouldn’t be there if the choice was just another version of Coke or Pepsi, paper or plastic, ribbed or French tickler.does at all not undermine the similarity: ethical beliefs are just those beliefs to which we have a greater emotional attachment than to mere taste beliefs.
(Also notice Steve's clever rhetorical technique of shifting from "akin to", expressing similarity, to "just another version of", expressing identity. This is a very effective rhetorical technique, and any intellectual reader should make a special effort to be alert for it.)
Steve correctly notes that, "In cases of deep moral doubt, we don’t just feel, we think." Again, this observation does not at all undermine MESR. Consider the analogy to taste again: I very much enjoy real ice cream (the artificially sweetened version makes me gag), but I also have diabetes and I very much enjoy being healthy. The fact that I have to think to resolve this discrepancy in my tastes does not at all undermine that the underlying discrepancy is still a subjective discrepancy.
The existence of convincing ethical arguments also does not necessarily undermine subjectivism (although it might do so). There are two types of rational arguments that do not undermine subjectivism: (1) arguments rationalizing competing ethical beliefs and (2) arguments about the means to achieve ethical beliefs by manipulating objective reality. To make this objection stick, Steve must show that an ethical argument can succeed by convincing us of the truth of an objective ethical statement contrary to our subjective beliefs (in, for instance, the arguments from evidence for quantum mechanics convince us to overturn our intuitive beliefs about the classical nature of reality).
The sense of Steve's essay seems to imply that MESR renders us entirely mute, that it eliminates ethical discourse. "[W]e would each be sequestered in our own little ethical bubble where it doesn’t matter how reasonable or wacko the folks in the surrounding bubbles are." But this is simply not the case. All that MESR eliminates is objective truth-finding discourse. It still permits rational discourse helping us to rationalize our discrepant and competing ethical beliefs and still permits objective discourse on how to achieve our ethical beliefs.
Furthermore, there are two modes of discourse we can apply to ethical disputes which do not depend on fundamentally finding objective ethical truths: propaganda and negotiation. Propaganda aims to directly change a person's subjective beliefs. Negotiation attempts to find a course of action acceptable in the face of competing ethical beliefs. Again, to use the metaphor of taste, if I want to eat Chinese food and my wife wants to eat Italian, we do not attempt to resolve the issue by deciding which is "objectively" better. We negotiate how we are to best fulfill our competing desires (and, with all good luck, remain married). We might decide, for instance to eat Italian tonight and Chinese next week.
Caging and Framing Tolerance
The idea that subjectivism or relativism entails absolute tolerance is not (outside perhaps academic philosophy) a position actually held by very many more-or-less subjectivist liberals in real life. Absolute tolerance is an idea flogged like crazy by authoritarian conservatives to undermine liberal challenges to their authority. A vast majority of liberals in real life hold Steve's sensible approach to tolerance, "Sometimes justice, fairness, and even promotion of tolerance itself require taking actions that do not place tolerance at the forefront. Tolerance is an important thing, but not the only important thing."
More importantly, this view is not at all contradictory to MESR: A person can have just this view of tolerance on purely subjective grounds. It is only when the fallacious enthymeme noted above is implied that absolute tolerance becomes entailed.
Essentially, conservative objectivist authoritarians have framed the issue of ethical relativism and subjectivism in terms of this fallaciously nihilistic view and caged the discussion to talk about only these aspects.
It's disappointing that the author of this essay would so easily fall for just the technique he so perspicaciously describes.
 For the annoying particularists, actualizing a ethically preferred state of affairs.