Well, first of all, what is the legal status of being a spam receiver, which I take it is what you mean by a porn site solicitation? That's still up in the air SFAIK. Meeting all three requirements in a legal sense wouldn't be easy, and even if successful it doesn't mean much in most jurisdictions of which I am aware.|
Second, spam is rarely sent from the same address one is being solicited for (I haven't seen that in years), so who is the offending party, the sender or the site? Proving they are the same entity, particularily when they often aren't because porn sites (and others like Amazon.com) pay an affiliate fee for a referral, the porn site may be blameless, and many of those using affiliates, including many porn sites, will remove, and normally refuse to pay, affiliates who spam.
Third, tracing spam back to its source is normally done via IP address, not domain name. The latter can be easily faked (and normally is) in the headers, the former less so, and the IP WHOIS will not normally give you information that directly points to the culprit, one must complain to the IP block maintainer. Even if the domain name is accurate, few spammers include accurate information in the WHOIS.
Fourth, spam which sends you to a particular website often uses a redirect to forward you on through one or a series of other sites, so again, who is the offending party, and again assuming they were truthful in the WHOIS?
Fifth, much of the spam I see points either to a site by IP number (it isn't even necessary to have a domain name), or is obfuscated in such a way that it takes tools most people (certainly most on AOL) don't know about to decipher it.
In short, your hypothetical example doesn't much match the real world, except that many people complain about spam from parties who are innocent. -g