In 2012, I replaced an often-hotlinked image with a picture of something gross, just on principle.

Be ready to be surprised, the next link to a meme you click could be a gore-fest.

sheez man

Not true.

Some of us are still on shared servers or have limited bandwidth, or just care on principle.

When the leechers are popular forums it can be a definite tax.

Making a local thumbnail isn't that difficult, likely in whatever language you happen to use.

I would care. There's no excuse for your site affecting my server in any way. If it's a site that gets enough traffic the number of connections being made to my web server for a single resource could be enough to adversely affect my site. Besides why are you going to take the chance that the image stays online and in its current location. Just rehost it, it takes such a minuscule amount of effort.