I'm sure some will take umbrage with my view, but universities typically embrace free speech and encourage students to challenge their own opinions and assumptions.
Even if someone disagrees with Jehovah's Witnesses, or feels their teachings and practices are harmful, unless they are somehow illegal, I don't see any problem with them having a presence on campus.
If a student feels like killing another human is wrong, should the university ban the U.S. armed forces from hosting a table at the student center?
If Westboro Baptist or Jehovah's Witnesses want a table on campus...my opinion is, let them. The students can judge for themselves and use their freedom of speech to react to it as they see fit.
Barring free speech on a college campus is far from most institutions' ideals.