But how do you draw the line between garbage content and quality content?

By your own subjective standards. We do not need to have totalitarian rules on this, the consensus emerges from the individual and independent votes of all interested stakeholders.

What you advocate for in essence leads to censorship.

Not so. Removing some potential financial rewards by down voting is not censorship. It is showing the market value of the post to be less than it was a previous point in time when the opinion of another stakeholder is factored in.