IMHO if invited by a student group,
"2) If a liberal or conservative speaker is invited, s/he must not be uninvited solely because the speaker might offend some student group's sensitive ears?"

Over time opposing views will be presented as different groups will invite different speakers. 

But if invited by the administration of a public institution, some effort should be made to present all viewpoints.  Not necessarily concurrently, but over time different speakers should be asked.