You should. There are a few aspects to this. 1) You should feel free to say what you want when you want. 2) The more you express support for feminist issues and HOF positions in particular, the more you will be identified with HOF and thereby discounted by some. 3) If you don't want to post in a contentious thread, you can still make a contribution. This heated threads tend to result in a lot of alerts coming from all sides. If a lot of feminists are involved in a thread, that means none of us can serve as jurors in those threads. That means posts by us are more likely to be hidden that those by people attacking feminists. Lately some of us have wondered if some of the members less welcoming to feminists might deliberately stay out of threads to make themselves available for jury duty on those threads. Of course, they might just not want to enter into the fray. But my point is that even if you don't feel like posting, you can still make a contribution my making yourself available for jury duty (click around the forums a lot, for example. As your post count increases, you'll be called for more juries). It's ultimately up to you. You should say what you want but don't feel compelled to jump in if you don't want to.
As for the silent majority, I really don't know. Numbers of recs seem to support feminist views on this site, while jury verdicts too often do not. I see more people making themselves available for jury duty. Hopefully that will help. Juries really are the power on the site.