It started being enforced only after major USA ISPs started injecting malware into every HTTP page. If it was a theoretical concern I might agree with you, but in reality, it actually happened which overrules any theoretical arguments. Also, PRISM.
PRISM works fine to recover HTTPS-protected communications. If anything NSA would be happier if every site they could use PRISM on used HTTPS, that's simply in keeping with NOBUS principles.
They collect it straight from the company after it's already been transmitted. It's not a wiretap, it's more akin to an automated subpoena enforcement.
