I think its unfair to argue that just because their viewpoints are in part shared with other groups that some consider undesirable that they should abandon or be ashamed of those viewpoints simply because any advancement in those areas would possibly benefit aforementioned undesirable groups as well.

Groups with wildly different goals can share similar viewpoints, that does not make them allies. The reasoning behind their platforms are not identical, and the desired outcome is unlikely to be identical, even though there is similarity in some aspects of their positions.

Let's say there's Group A:

    - Advocates for abortion rights
    - Ethically and medically opposed to carnivorous diets
    - Requires wearing of a fez and monocle when out in public at all times

Group B:

    - Advocates against abortion
    - Opposed to carnivorous diets because eating the souls animals may increase the chance of spontaneous combustion
    - Condemns the fez as an abomination against all mankind; doesn't know what a monocle is, still considering boycott for symmetry's sake

Those two groups are at odds in many respects, but do share a dislike for flesh mongers.

What if a member of as yet defined Group C tries to persuade a member of Group A to abandon as aspect of their platform by saying, "I suspect you have little in common with those Antifez jerks in any other way. So why would you want to fight this particular battle along side them?"

That seems like an unnecessarily combative stance to take. Comparing Catherine MacKinnon to Islamic extremists or to unreasonably homophobic Russians is for sure hyperbolic.