I mean, I'm not wholly convinced of their explanation of why they did it, but I agree on one thing: you wanna do this, start somewhere new to "iterate." I sort of refuse to believe they didn't understand the community they were messing with when they announced this. It's not that I think they wanted to actively destroy the fan-based modding community and control of content.
But I think they weren't really concerned about what would happen to it if paid mods for Skyrim had taken off, which is arguably just as bad. "Look, I don't want to crush your house with my steamroller while I'm building my super highway. I've got nothing against you. But if it happens to be in the way and I roll over two corners of it, well, sorry, that's business." I think Valve and Bethesda were trying to capitalize on the informal nature of the mod scene, like they thought no one would notice a dude in a suit with a briefcase full of money and a consent form walk into the room.
Anyways, I was also feeling pretty confident that Valve would back off. But I wouldn't celebrate. All that's happened is someone has tipped their hand to the next revenue stream idea. This will be back.
The biggest problem to me overall with paying for mods is the lack of enforcement. Not even Nexus would probably have the power to police all the submissions for infringement and outright theft. The overhead burden user-generated content can introduce for whoever is responsible for it can be enormous. And I don't really see how they're going to get around that, being responsible for the content they essentially buy from the user at cut rate prices. For the companies that seem to care so deeply about intellectual property, they seem to have zero respect or understanding of it when it's not theirs.
TLDR: I pretty much refuse to believe people that make this much money simply didn't think about the ramifications, legal and social, of what they were doing. I'm starting to feel about Valve and Steam like I do about my cable company: a necessary evil.