If you are participant of the Gitlab community, you could speak up in that thread and say that you are not OK with people being insulted over a disagreement. I won't fault you for not wanting to, though. You would probably be attacked too, and have to spend a few hours of your life justifying yourself.
There is a keen difference between criticizing it and forbidding it. Gitlab may forbid it on their platform, but they don't have the ability, let alone right, to regulate the speech of the general public outside their platform.
