First of all, you shouldn't try to "shut up" people who promote Windows. They
have a right to express their views just as much as you.
Now, as to dealing with people who don't agree with the libre software
movement or even necessarily know about it, it's complicated. As
ssdclickofdeath said, don't join a community just to criticize them for their
views on software. I don't think you'll necessarily come across as a troll,
but you will come across as a desperate street preacher of sorts. But if
you're already a part of the community for a different reason, I think it's
OK to bring the libre software position up as long as it's relevant. Based on
my attempts to do this in the past, I think the important thing is to
suggest, through context, that you are interested in debating the merits of
your views, and then follow through with a pleasant debate if someone else
challenges you. Be strong and firm, but respectful.
For the record, I don't think it would be appropriate at all to bring up
libre software in this particular topic. It's a topic asking for suggestions
of Windows versions to use. Bursting into topics that are supportive of
proprietary software and saying that it's bad is not helpful. The sorts of
times when I would bring up libre software are e.g. when a malicious feature
in a proprietary program is being discussed, when open source is being
discussed, or when various alternative programs that do a particular job are
discussed.
