"pirated themes" - that wording is not very useful and it's not clear what this means. Sounds like FUD to me.

Those sourcecodes under proprietary licenses that you can find somewhere are sort of a license-bomb for potential users. In the moment they mix it with wordpress code, they loose the right to use wordpress if it's not GPL compatible.

And most often these theme "creators" are not only careless about licensing but as well they don't care about their users. So I would stay away from obfuscated themes at all cost in the first place. If you find a nice guy who can decompile it for you, well that's nice. But users should be better educated about the problems these obfuscated themes bare in parallel.