Ok, but there is also no chance to logout to use "contact us" or just maybe read forum pages (clear cookies etc.)
Banned user has no chance to be a user any more - ok. But imagine that you make a mistake and ban wrong user or two... What should those users do to indicate an error happening?
This system has no responsiveness and a chance to correct what was done wrong
It looks like "Any feedback, anyone? " ...
All valid websites have a list of emails that should be setup when the site is open to the public. email@example.com is one of them. As for spam, well your email server should be setup to deal with spam. Personally, I use gmail to access most of my private emails such as that. So setting up a decent spam filter is rather easy.
If you want your users to know about the email, you could change the default message that is emailed to a user when they're banned and make sure that you check the box to send them the email when you ban someone.