Parliament rejecting a speaker is not the same as a university rejecting a speaker. Parliament does so as a political gesture. Bercow barred Trump from speaking as a gesture of protest that the House of Commons was opposed to his Muslim ban.
Universities are not there to make political statements, they are there to further human comprehension and understanding. They are also there to educate students and inspire. These roles demand that universities engage with a wide range of ideas to ignite healthy debate, challenge students, and enhance human progress and understanding.