The thing is, the more you try to prevent people to do something, the more imagination they use to work around it. Let's take the word "****" (the s-word).

Some will try to write it plain:
" " and it looks silly

Some will use stars:
"s*it"
"sh*t" (the most common over the web, I think)
"s**t"
etc...
There's always or any variations thereof.

Or smartasses (:E) will trick the filter:
"Shit", said the word filter. "I'm tricked".

So, to make it short, I agree with Unne.
xD