> did not respect our robots.txt

I don't see a problem

> ignored our Terms of Service

ban them from the service then and case closed?

> and defied the creators' licenses: 423 of the 712 projects are licensed for non-commercial use only

because it's been proven they have been used commercially?

I do. It's wrong to ignore a robots.txt.

The fact someone else may have licenced content for commercial use doesn't entitle someone else to do the same without paying for it. That's the whole point of copyright law.