This kind of argument pops up all the time whenever a subreddit has a discussion about moderation but in my experience it doesn't work in practice. For starters, only are there technical disparities between what the rating algorithm considers hot and what the community actually likes (for example, images can get lots of quick votes soon after submission, which propells them to the front page). But perhaps even more importantly, there is the "eternal september problem": moderation lets a subreddit enforce their culture to the new users, which is very important. Something like /r/askscience would be impossible to maintain in its current state with just user voting.

As for tagging, it helps in some situations but its not an universal solution. The UI is kind of lacking (you need a 3rd party extantion to hide unwanted tags and it doesnt filter posts in the reddit.com frontpage) but it also doesnt do anything for passing users who havent configured their tags.

In a hypothetical world maybe its possible to create a smarter "hotness" algorithm that is less prone to these problems but in the current system I really don't think "just downvote the bad stuff" is a practical solution.