To me the karma system is about quality. Not an “I agree/disagree” button.

That's how it was meant to be. The original Rediquette from over 15 years ago has:

"Vote. If you think something contributes to conversation, upvote it. If you think it does not contribute to the subreddit it is posted in or is off-topic in a particular community, downvote it.
[Please don't] Downvote an otherwise acceptable post because you don't personally like it. Think before you downvote and take a moment to ensure you're downvoting someone because they are not contributing to the community dialogue or discussion. If you simply take a moment to stop, think and examine your reasons for downvoting, rather than doing so out of an emotional reaction, you will ensure that your downvotes are given for good reasons."

But 99% of people definitely use them as an Agree/Disagree button.