I think there is a lot, lot more to this vexed question than (as this post implies) people who want free stuff and think it should be free because they imagine it's easy to make.
Remember, some of the most outspoken voices against paid-for mods have been very capable and accomplished modders who know exactly how much work goes into their hobby.
There are serious questions about the whole ethos of switching from a hobby where hitherto there's been no commercial aspect, to one where there are contracts, obligations to customers, expectations of quality and mods being 'fit for purpose', commercial competition and rivalry between modders, financial harm (direct and through damage to reputation) from copyright theft, and all the other issues that can go with business ventures.
The fact that some people undeniably want free stuff which they've enjoyed up until now doesn't remove the fact that this would be a very big change which would have to be managed with great care and sensitivity, if the atmosphere of sharing and co-operation that the mod making and using community has enjoyed (with, admittedly, it's own problems) up until now isn't to be wrecked.
Personally I think that paid-for mods could be done, and done well. The way it was handled before and the enormous ill feeling (and bad press coverage) that generated, makes me think that Valve and probably Bethesda aren't the ones to do it. At least... not for a long time.