The premise is mistaken: this is not a shift in the quality of the site. People have always voted based on their own personal, irrational reasons. The sentiment is noble, but never fear: the system has always suffered this abuse, and yet it has continued to work.
See the variety of reasons for voting that people express in these MSO answers:
- What do votes mean?What do votes mean?
- Why do you cast downvotes on answers?Why do you cast downvotes on answers?
- How should down voting be used?How should down voting be used?
- Why should I upvote a question?Why should I upvote a question?
- What purpose does downvoting questions serve?What purpose does downvoting questions serve?
… and lots others I couldn't find with an easy search.
That said, I entirely agree that downvotes don't obligate a comment. I don't think it's a fight worth fighting though: so long as the site doesn't require downvotes to have a comment (which it never will), the majority will continue to happily ignore other users who insist downvotes need comments.