Good question. The documentation says:

On the left side of each post there are up and down arrows, which let you upvote or downvote it. You can upvote posts that you like so that more users will see them. Or downvote posts so that they are less likely to be seen.

which doesn’t really back me up.

My downvote principle was meant more generally - most places that have a downvote policy say that it’s not meant for shouting down people you disagree with, since that’s not conducive for civil and balanced conversations.