This is a really tricky legal area. There have been a very limited number of real cases involving EULA terms like this (and I'm not sure any have been decided at a trial), and there will be wide variability between jurisdictions.
You can, in principle, contract away your right to speak on a well-defined subject, at least in the USA (I believe all common law jurisdictions permit this to one degree or another). Consider NDAs, for example.
What terms like these get into, however, is a question of fairness and equity. Terms that are almost certain to come up in common law jurisdictions are "contract of adhesion", "unconscionability", "fair dealing", and most importantly, "consideration".
Just skim the Wikipedia entries for those terms and you'll quickly see how complex and subjective this gets.
You can, in principle, contract away your right to speak on a well-defined subject, at least in the USA (I believe all common law jurisdictions permit this to one degree or another). Consider NDAs, for example.
What terms like these get into, however, is a question of fairness and equity. Terms that are almost certain to come up in common law jurisdictions are "contract of adhesion", "unconscionability", "fair dealing", and most importantly, "consideration".
Just skim the Wikipedia entries for those terms and you'll quickly see how complex and subjective this gets.