Seems like a simple matter of signal to noise ratio to me. That single comment by itself does no real harm, but if it's not discouraged, the practice will proliferate.
The situations you cite do not include the potential for noise overwhelming the signal, so they are not analogous.
I know that a downvote can seem like a judgment on the person, but it's more a judgment on the action, and it can be instructive if taken that way.
[Edit: Not that I've been here that long, but that's how I understand the phenomenon.]
Sorry. It's definitely not my place to "enlighten" you. I don't want to be that kind of person.
I just am compelled to speak up for what I believe to be right. I didn't mean to sound like I was attacking your opinion, so in retrospect, I shouldn't be saying things like "I can say with absolute certainty..." I don't know anything for certain.
I just believe that the world is a nice place when people can simply say nice things to each other every once in awhile.
The situations you cite do not include the potential for noise overwhelming the signal, so they are not analogous.
I know that a downvote can seem like a judgment on the person, but it's more a judgment on the action, and it can be instructive if taken that way.
[Edit: Not that I've been here that long, but that's how I understand the phenomenon.]