There's a lot of words, but no data in these posts. The only argument is that sales are expected to decline very fast, so stopping piracy there is very efficient. I would argue it is quite dishonest to pretend Steam is popular because it is a DRM solution, it is popular with consumers because is is a convenient marketplace. It seems like confounding publisher and consumer mindset.

Conveniently, there isn't a single downside mentioned! Some games have stutter at launch or take a 20% performance hit, so there must be an impact on sales. Adding DRM is also far from free, it is always a good idea if you don't talk about the cost.

I would expect the picture to be quite different depending on the type of games/market. But these posts only show that there's a belief that it works.