I'm quite new around here, I've played maybe 200 games in total - mostly unrated 1v1 practice games that I host. Although it's a bit of an unusual environment, I've faced players from all over the world with ratings from -100 to over 2k.
I can happily say that almost all of my games ended with a "gg" and in many cases also additional words of advice from better players after the match. The most toxic thing done to me was a first bomber
The situation might be different in stressful teamgames but from my newbie perspective the community is solid.