First, homophobic posts shouldn't be tolerated on a site that calls itself progressive, any more than anti-choice posts. The tolerance of homophobic posts doesn't validate the tolerance for anti-choice posts. It just means DU is doubly wrong.
For your other analogies, when someone says that they are opposed to affirmative action or they don't believe white privilege exists, those are very different from saying "we need to outlaw abortion."
I have no problem with someone saying, "I don't believe in abortion" as long as they are speaking for themselves. I will disagree and discuss, as I will disagree and discuss with someone who is against affirmative action, or who denies white privilege.
A more accurate analogy to the statement "we need to end abortion rights" would be much more extreme than denial of white privilege or arguments against affirmative action. It would be more along the lines of someone saying, "we need to end the self-determination rights of minorities. We need to overturn Civil Rights legislation." That's very, very different.
But when someone on DU joins the strengthening ranks of people who say "we need to outlaw abortion," they are advocating taking away the self-determination, the basic civil rights, of half the population.
They are saying that the state should dictate how the bodies of half the population are used, against the will of those who inhabit those bodies.
They are consigning people to poverty, underemployment and astonishing mental anguish from a thousand different sources.
And right now, that basic civil right to self-determination is being assaulted from all sides, and the assaults are gaining strength at an alarming speed. A site that contributes to the voice and power of those assaults has no right to call itself progressive.