Would you join a Subreddit which reinforces these political beliefs and is that not a safe space in itself?If I understand your question, yes. I would join such a Subreddit because an echo-chamber isn't what I seek.
I completely agree with forbidding things like doxing or making threats of violence but I'm concerned that "Safe spaces" only encourage intolerance towards other points of view.
Disagreement is good. Maybe I'm wrong and you can show me a side that I had never considered. Maybe you're wrong and I can present an argument that changes how you think about something. I have had my mind changed by a persuasive argument in the past. Perhaps I will again in the future. I have friends that I have seen change their views over time and I hope that I was at least a part of what caused them to change on those issues.