The argument against Divine Command Theory — if God commands X, then X is good by definition — is very simple.
There are only two cases: Either God commands only what conforms to our independent judgment, or God commands some activities contrary to our independent judgment.
The former case is vacuous. Divine Command Theory adds nothing to our independent judgment: we can rely directly on our independent judgment without talking about God. At best, Divine Command Theory becomes merely a terrible ontological theory to pretend to explain why we independently make certain judgments. It is no longer an epistemic theory: we don't know, learn or discover how we should exercise our judgment — distinct from how we do in fact make judgments — by examining God's commands.
The latter case is problematic. If we believe that God makes some commands contrary to our independent judgment, how are we to respond to those commands? More importantly, how are we to distinguish authentic commands from fake commands? How are we to distinguish between commands that are dependent on some particular context and commands that are independent of context? By definition, since we are accepting a priori that God's commands can differ from our own independent judgment, we cannot use our independent judgment to distinguish authentic commands from fake commands. Similarly, we cannot use our independent judgment to distinguish what elements of context are relevant to a particular command.
Any exegesis of any scripture other than absolute literalism requires the exercise of our independent judgment. But if we can reliably use our independent judgment to interpret commands, why not rely fully on our independent judgment? On the other hand, if our independent judgment is not sufficiently reliable to rely on fully, by what virtue do we rely on it to distinguish authentic commands from fake commands? By what virtue do we rely on our a priori unreliable independent judgment to pick out those elements of context relevant to the command?
The only way to avoid hypocrisy is to grasp the nettle: fix on some scripture, and take every moral commandment literally, completely independent of context unless that element of context is explicitly, unequivocally stated in the scripture itself. Any attempt to do otherwise is hypocritical bullshit sophistry.