They can't be thta stupid. If I'm not buying insurance, then there's no "commerce". And if I am buying insurance, that would be "commerce", but I'm prohibited by law from buying it a in a state I don't live in. So that wouldn't be "interstate commerce".
ANd if Congress is to provide the general welfare, whwre's my food? and clothes? etc..
I had a long dissertation posted a while back. Insurance is a service and does not fall under the commerce clause.