If you believe that destroying books is bad, your issue is with copyright law, not the AI companies. The AI companies are just following copyright law -- they are allowed to move data from one format to another (thereby destroying the original), but not copy it.
Not everything objectionable or unethical should or could necessarily be outlawed. "It's not illegal" is not really an argument or justification for anything.
I don't think CaptainFever's point is that it's acceptable because it's legal, but rather that copyright law is what prevents them from, say, donating the originals instead of throwing them away.
