Yes. That's not perfect. But it raises the bar for forgery to "can sign certificates as a root authority", which is still fairly high. (e.g. I can't do it, and neither can you.) It stops coffee shop/hotel wifi operators and mobile providers from injecting content into your session.

If we encourage users to blindly accept self-signed certificates (giving us end-to-end encryption but sacrificing identification), nothing would stop those actors from altering your HTTPS sessions as easily as they alter your HTTP sessions today. It's throwing the baby out with the bathwater.

This is true for most sites now, but is being solved gradually, with hard-coded certificate pinning already shipping in Firefox and Chrome, and the HTTP Public Key Pinning extension coming soon.