I agree, but I'm not sure that it couldn't be forced. We pass regulations on businesses all the time, including the porn industry. Why not force them to have the .xxx domain?
It isn't as much a regulation problem as much as a definitional problem. How do you define "porn" or whatever material requires the xxx designation? I've stumbled across sites that have an adult content warning, which I don't know if it is required for their content or not. Perhaps if it is, there's your answer -- anything with an adult content warning = XXX. I think what some people might not like is sites that might have nude pictures (i.e. photo sites or nudist sites) being required to be a XXX.
Frankly, that is the ONLY way to make filtering effective. Of course, the smut peddlers will cry over the cost of changing everything, to which I say "SO??". We had the area codes in NC changed twice in the span of a few years and businesses all over the state (except for the Capital, of course) had to change letterhead, business cards, etc. We hear about how profitable the porn business is, so what is this minimal cost to them? Not much.
They also say they aren't trying to target kids, well, this would prove it. Let ANY website that has access to nude pictures of anyone be required to use the .xxx domain. This would also discourage linking to illicit pictures on message boards and prevent some kid from putting up a personal site and giving his "friends" access to his porn scans.
If someone does put up a site where people can access nude pictures or worse, they get hit with a fine for the first offense. If they don't change or take it down within a certain time period, a BIG fine. If they do it again, or fail to take it down after another designated time, they get time in Pound-Me-In-The-Rump Prison, where their "fans" can show their appreciation for the person's handiwork.
Sorry, I work in IT and have NO tolerance for some of these smut peddlers. Access for kids to all kinds of stuff is way too easy and something needs to be done to make it more difficult.
It probably COULD be forced (if we eliminated non complying 3rd party nations from being able to sell .xxx names, and limited which ips could register).