If a browser didn't display images, would that be a bug? I don't see how images in emails are any different. I never send HTML emails myself, but I do receive them, and I want to be able to read them.

I agree completely with the security issue, which is why I've not enabled the download process on my modest.

Adding an option to make it at user's preference -> enhancement
Not showing them at all -> bug

Anyway, this is my opinion, and I'm going to opine no more.