Compared to other platforms, they have a lot of good features and generally act in the public interest.

In regards to their DRM system, honestly some people are going to add DRM to their games no matter what. I’d much rather they use Valve’s system than some insecure third party spyware.

People have also mentioned their 30% cut which honestly seems pretty normal for an online storefront. It’s especially fair when you consider the fact that they provide marketing, hosting and payment processing for you. Not to mention things like achievements, matchmaking and workshop support if you want it.

There’s also the fact that a lot of the anti-monopoly folks tend to be Linux and/or foss advocates, and Valve has been pumping a lot of resources into open source projects.

Honestly, in the Linux space, the only reason Valve has a monopoly is because the other players just aren’t making any effort to compete.

Tl;dr Valve uses their market position for good (in general) and Steam is a good product.