Engels deliberately underlined the words "in relation to the state," as a straight thrust at German opportunism, which had declared religion to be a private matter in relation to the Party, thus degrading the party of the revolutionary proletariat to the level of the most vulgar "free-thinking" philistinism, which is prepared to allow a non-denominational status, but which renounces the Party struggle against the opium of religion which stupefies the people.
The struggle against religion cannot be made by any state (even a revolutionary state under the dictatorship of the proletariat) but there must still be a struggle against religion. Since the struggle should not be made by the state, it must be made by social propaganda, by polemic (a polemic is the opposite of an apologia).
I've been struggling in solidarity with the new "militant" atheists for a decade, and anyone who spends even a short amount of time collecting the actual facts, rather than relying on the lies and distortions of religious anti-atheist propaganda, fellow travelers and opportunists, can easily see that while most "new atheists" are not communists or socialists (they are predominantly mainstream liberals), our attitude reflects almost exactly Engels' and Lenin's. We must have legal secularism (indifference of the state to religion), but we must forthrightly and directly carry on the struggle against religion by social, polemical means.
As a side note, many socialists, anarchists and Utopian dreamers seem to have a difficult time grasping the concept that the new atheists really are freethinkers. The new atheist movement is deeply "ecumenical": no individual, however many books he's sold, speaks for anyone but himself. Specifically, even though Christopher Hitchens (and Sam Harris to a lesser extent) supports the U.S. imperialist war on Iraq and the Middle East, this support for imperialism is widely condemned by the mass of new atheists... without denying one whit the justified condemnation of Islam itself as reactionary, misogynist, despotic and fantastically ridiculous.