The line between "upvote for good point" and "upvote for agreement" can be blurry, same for downvoting.

In either case, both are accepted uses. PG has said as much:

https://news.ycombinator.com/item?id=117171

Interesting. I guess I was a bit too quick with my previous comment then.

However to me it feels a bit like discouraging alternative opinions, when they are hidden/greyed out.

Is this commonly accepted then?

Honest question: If not for showing agreement, what is the reason for the upvote button?

I thought it meant "nice contribution to the conversation". It's easy to come to this conclusion when you think down-vote means "you're not contributing". I up-voted many comments I totally disagree and down-voted many I agree (because they were unrelated to the discussion). Am I a minority?

Well, the HN guidelines[1] do not mention any rule as what constitutes 'right' voting criteria. As a regular HN user of over 6 years it feels even surreal to be in a discussion about the basic features of this wonderful platform. It's never wrong to question the basic premises of life, though(;

I do believe we have the a similar kind of understanding for when to up-vote. What is a 'nice contribution to the conversation' other than arguments or facts that 'I do agree with' in them being a nice contribution to the conversation.

I fear we would have to have a meta-discussion on the concepts of good and bad and how they are flawed in that there are no montains without valleys^^

1. https://news.ycombinator.com/newsguidelines.html

what's wrong with upvoting with agreement?

Upvoting based on "this comment brings up good points and arguments" rather than "this comment says things that I think are true" helps fight against the community becoming an echo chamber.

We downvote despite "good points and arguments".

The community is in many ways already an echo-chamber; that battle was lost a few years ago. Don't let it bug you.

Isn't "good" just as subjective as "things I think are true"?

The problem isn't subjectivity, it's groupthink. "Good but wrong" posts are better than "bad but correct".

Exactly. It's not that interesting to be in a forum where people are only awarded for being in line with the popular opinion. The alternative is to award constructive contributions.

+1 I agree.