Gitlab is a wonderful company, but it's still a for profit company, it's not a charity. Everything they're giving away for free is part of the business model, and particularly part of their user acquisition approach. They, and many other companies, have discovered that the open source (or in this case "open core") approach can be very profitable.

I'm not advocating in favor of rudeness, but the same reasoning goes for the middle finger gesture. It's an emoji that Gitlab have (I believe) deliberately included in their commenting mechanism. As far as I understand, it acts as a way to categorize users' anger and vitriol in a much more sanitized manner than if the users were to type their sentiment into the comment box. In general, allowing and encouraging negative feedback of specific parts of the service helps drive user engagement and demonstrably makes good business sense.

If users feel entitled and free to speak up, it's because there is a lot of competition in this area and they can easily leave. The fact that users are providing this feedback to Gitlab, rather than just deleting their users is a sign that they still trust the company and the service, want to keep using it and to drive it to be better.