It's not like that for me. Of course, negative feelings are floating about in the posts (especially venting, stories tags), but this is a forum of suicidal people, of course we're depressed. It's why we're suicidal in the first place.
Nonetheless, I think that the people can be encouraging and accepting without being patronizing/dismissive, more than any other place can be. The whole society tends to shy away from negative emotions; impose a forced/toxic positivity where they believe acting happy will lead to happiness. Suicidal thoughts are often countered with words like "dont think like that!" or "it will get better". This is the only site I can tell my feelings without fear of being dismissed, and I think thats valuable for people like us whose uncomfortable emotions isolate us from "normal", happy society.
In fact, what i like about ss is how its so non imposing. If you decided to ctb, people may ask if youre sure, but will ultimately respect your bodily autonomy and decisions. If you decided to back out, put it off, or give life another chance, the people on the site will cheer you on. The site respects people's decisions, and i dont know whats toxic about that.