Frowned upon the mainstream web.. yes.

My Bcentral mailer account was closed because it was adult. I didn't spam, my emails were all G-rated and to existing customers that signed up for my email notices. The specific reason given by Bcentral.. after mainy emails.. was because the site it linked to was adult oriented. Even though it was opt in from my own customers they still closed it.

A new hosting company I've looked into doesn't state in their terms that they don't accept adult but when I asked them via email specifically if they do, they don't respond, but they do respond to my other emails.

Adult internet is still taboo in the mainstream web.