When you impose rules which limit users' ability to do what they need for their business, you open the door for someone else to come in and service your customer instead, removing that customer from your income stream. That's my opinion anyways.

Let's say I was a Registrar and I indicated that no domains could be registered through my service if they were "vulgar" in nature. As soon as one of my clients wanted to register such a name and found that they could not through my service, they're off to another service and will likely register all future domains with the new service. That may be a bad example because some folks don't care to have certain names in their database and the lost money means nothing to them. Fine, let's try another example:

Shell access used to be a staple in the hosting environment but many companies have turned off that feature for security purposes or some misunderstanding of how things can work. So if you don't offer shell access and someone needs to SSH into their machine, they'll simply leave and find a service which provides what they need. If other companies did not provide the service you can bet that someone would jump in and fill that gap pretty quickly.

Now let's look at the large ad networks out there; Google and Yahoo!. They've become fairly hostile towards individuals with a plain 'ol parked page. Sure, it can be done if you're large enough or if you go through an aggregator but for the folks with just a handful of domains, they're making it tough. I wonder what is going to happen? I wonder what monster of an advertising facilitator is going to fill the gap? What do GOOG and Y! have to lose? Well, the little guy may very well turn into a big guy, but he's already been chased away. And, this new monster company may woo other huge advertisers away form the two staples. It's opening the door and I think the two biggies are going to be left with tremendous feelings of regret for having pissed on the [for now] little guys. I could be wrong but my guess is that AdBrite or some other soon to be monster stands to gain quite a bit from the policies imposed by the biggies.