In my opinion, this comes very close to "censoring" content.
That's great that GitLab believes in responsible disclosure, but that doesn't mean that everyone does or that you get to force your beliefs on your users or customers.
If you do in fact plan to censor content then you need to be very clear about that up front and identify what types of content you will not permit.
I'm glad that GitLab has done a 180 and reinstated the content. In the future, I hope they will fully think through any decisions to pull down content that they don't "agree with". I do give them credit for recognizing they made a bad call and admitting to it.