Steam is a private company and has the philosophy that they do not want to tell you what you can/cannot buy.
What is quality to someone, will be garbage to another. it is a subjective issue, not an objective one.
Well that's why they are deciding what you can or cannot buy in their store.
It's their prerogative where they chose to set the bar. In this case they chose to set the bar very low. Allowing you to buy virtually anything.
Any game that they wouldn't have allowed on their store would always be purchasable somewhere else. But it would have been understandable for any company if they want to make that choice. However, Steam doesn't really have any real competition, and this decision takes away another potential incentive for customers to chose a competitor's service.
I get what you're saying though. You want to be able to buy as many games as possible because you want the deciding factor to be your own judgement. It's just the way you said it.
As for me, I think I'm on the side of more quality control. Not for my own sake because I think I can properly judge if a game is for me or not. But rather for people who are not particularly good at it. Though at the same time, I would also like the bar to be set rather low, because one of the things I liked about PS2 was that it had so much of everything. And I found some nice gems in obscure titles.
I still don't understand how Sony allowed Life of Black Tiger on PS4. They even promoted it with a trailer from the official Playstation youtube account. And I feel a bit bad for anyone who spent money on it unwittingly, because I have a hard time believing they wouldn't have gotten a lot more enjoyment out of their money from another product.