It is difficult to say whether you should sue or not, but here's some ideas about where to start. The first part of the analysis is whether the school is public or private. Students at public school generally have more rights. You should also analyze the student code of conduct or any other contract you may have signed and see whether the school is violating its own rules by removing you from the school.
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I just wanted to add that there are two organizations that it be worth you consulting: (1) The American Civil Liberties Union (ACLU), and (2) the Foundation for Individual Rights in Education (FIRE). The former is thought of as "liberal" and the latter as "libertarian" but they often agree on campus free-speech issues and both have helped students and faculty with these matters.
The website for the ACLU is http://www.aclu.org/ and FIRE's is http://www.thefire.org/article/5063.html. In addition, FIRE has a guide to free speech issues on campus that you might find useful. http://www.thefire.org/public/pdfs/free-speech.pdf