You're probably right. However, I'd guess that anyone subjected to such a ban would not want the extra publicity of challenging it in court, not the cost of legal representation.
Most clubs have a clause about bringing the club's name into disrepute in their season ticket terms. Whether or not this would be enforceable if it were challenged legally is another matter.
I agree with you. They will however be punished by virtue of their names being in the public domain. I can't imagine their current (or future) employers will be very impressed, and any football clubs they support - whether that be Palace or whoever - will want to dissassociate themselves with...