It's a much bigger challenge, and I find it wildly cavalier for anyone to say "just use HTTPS everywhere" without directly addressing the faults pointed out by others. And by addressing, I don't mean dismissing out of hand.
Hell, I'd settle for acknowledging instead of addressing some days. There are real world problems on both sides that need to be considered.
But these are two separate issues. Going from plain HTTP and HTTPS to HTTPS-only is a step in the right direction. It's also step 1. Step 2 is to drop CA's and work out a better trust system that relies on less parties being involved.
Also, let's give people some credit. Yes, some people ignore the self-signed cert warning. Some people also respond to Nigerian prince emails. We aren't talking about cutting off email because someone might get hurt. Unless you are ready to drop all untrusted certs, those dialogs need to stay in place.