I agree with you that people can get pretty worked up about the topic of free software, but I think you need to be a bit braver in the face of downvoting and disagreement. I can't ever recall seeing a respectful, well-thought post getting downvoted below 0 on hacker news.

One tactic for this situation is to post your truth then never look at the thread again. It might be rude to people who want to engage in honest discussion on your point, but if your post was a good one it will still benefit the hn community more than not posting at all, and you won't have to stress about troll replies.

Just be respectful. Assume the people reading your post are as smart as you and your post won't get hammered.