There are two levels to this debate, I suppose, the more abstract discussion of principle and the concrete example of Savage himself. I'll start with the former because it eventually directly leads into the latter:
I don't think this is a freedom of speech issue. Freedom of speech a nationally internal concept: it's the idea that you can say whatever you want (with few limitations) without being persecuted by your own government. It's very funny that an opponent of illegal immigration who is constantly comparing the lack of an airtight border to "suicide" is now complaining that England is reserving the right to keep him out. I'm pretty sure he's also argued that the President of Iran shouldn't have been allowed on US soil about a year back as well. No, he's not as bad as the President of Iran (only because he's lacking the power to do anything too horrific in my mind), but if you expose the right to exclude undesirable persons in one instance, then you have to agree with the general principle enough that it being applied towards you comes down to a judgment call (and thus the second part of my argument).
Now for the more important discussion: Michael Savage is a hateful, idiotic, bigot of the highest order. There are few issues this guy isn't on the wrong side of. On his show he regularly goes into blatantly racist rants (often insulting minorities I've never even heard of -- what is a mung?), complains about the direction the country is taking socially while slandering people who live in anything but a 1950s lifestyle of delusional self-oppression, says all sorts of scientifically ridiculous things (he's a homeopath and doesn't believe in Global Warming because "carbon dioxide" is needed by plants, and that's literally his whole argument), and worst of all he passes off his beliefs as if they're educated and intelligent with his "Dr." moniker (and nearly 100% of the time the opinions he's professing are either outdated or completely out of his area of study).
He likes to refer to liberalism as a "mental disorder," claims that the pornography industry is destroying the country by weakening men and convincing the youth that casual sex is both consequence free and a virtue. His opinion on Islam (which is the specific reason he was banned) is especially inflammatory: he essentially believes in no compromise, thinks moderate Muslims are a myth, and regularly says incredibly hateful things towards the religion as a whole.
You know what this post needs? Quotes. I wish I could put up some fine classical music in the background why you read this, in fact, I think I'll pull up something on Youtube. Here you go:(BWV 847) Bach: Prelude and Fugue in C Minor, WTC I (equal durations)
Savage on homosexuals: "Oh, so you're one of those sodomites. You should only get AIDS and die, you pig; how's that? Why don't you see if you can sue me, you pig? You got nothing better to do than to put me down, you piece of garbage? You got nothing to do today? Go eat a sausage, and choke on it. Get trichinosis. Now do we have another nice caller here who's busy because he didn't have a nice night in the bathhouse who's angry at me today? Put another, put another sodomite on....no more calls?...I don't care about these bums; they mean nothing to me. They're all sausages"
Savage on Autism: "Now, the illness du jour is autism. You know what autism is? I'll tell you what autism is. In 99 percent of the cases, it's a brat who hasn't been told to cut the act out. That's what autism is. What do you mean they scream and they're silent? They don't have a father around to tell them, 'Don't act like a moron. You'll get nowhere in life. Stop acting like a putz. Straighten up. Act like a man. Don't sit there crying and screaming, idiot.'"
Savage on Science, Liberals, and drugs: "Every day, brainwashing 'til you don't know the difference between right and wrong, family and a fake family, real science and morons who are on drugs inventing science -- science fiction, that is. You don't know anything anymore in this country. You've been brainwashed by the liberal elite -- the establishment -- if you want to call them elite. How can you call drug addicts elite?"
Savage on Immigrant Students: "Then there's the story of college students who are fasting out here in the Bay Area. They're illegal aliens and they want green cards simply because they're students. I don't understand what -- how this two and two adds up. I would say, let them fast until they starve to death, then that solves the problem. Because then we won't have a problem about giving them green cards because they're illegal aliens; they don't belong here to begin with. They broke into the country; they're criminals. Why do I owe them a green card? Because they're going to my colleges for free?"
Savage on Valueless Immigrants and European Supremacy: "...when you bring immigrants in from Europe -- whether they be Irish, whether they be Italian, whether they be English, whether they be Romanian, whether they be Czechoslovakian, whether they be Yugoslavian, whether they be German -- they're from Europe, and there is a melting pot possibility... When you start bringing in masses of immigrants from everywhere on Earth, you don't have a melting pot; they cannot be melted into an American, and that's what's going on in the country today. We're bringing in millions of people from countries that have no compatibility with the values of Europe, not any values whatsoever."
Savage on Islam: "The Islamists smell weakness in the West and are attacking us on several fronts at once: one, through outright war; two, through immigration; three, through their propaganda disseminated through the liberal media and four, through the liberal courts. Only a devastating military blow against the hearts of Islamic terror coupled with an outright ban on Muslim immigration, laws making the dissemination of enemy propaganda illegal, and the uncoupling of the liberal ACLU can save the United States. I would also make the construction of mosques illegal in America and the speaking of English only in the streets of the United States the law."
By the way, his name isn't even savage, it's Weiner. He changed it because he wanted to be more hardcore. Thug life, ya'll.