You can possibly get your case dismissed. It's not going to be easy, however. If you're stating unpopular opinion at school, generally speaking, you should have a right to do. That being said, a student does have certain expectations and obligations to meet under a school's code of conduct and potentially otherwise. It really depends on what the specifics of that unpopular opinion would be in terms of whether the school is within his rights to pursue disciplinary action or not.
Unfortunately, schools are often overzealous in terms of pursuing disciplinary action for a student who is just otherwise expressing free discourse, or just say engaging in the academic process or the learning process by saying something in class or by posting something online. It depends on the circumstances in terms of whether the school is going to be within its rights or not. You cannot depend on the school to do the right thing. Having an experienced attorney advisor will be your best ally and will help you understand and navigate the process to work towards what hopefully would be appropriate to the circumstances, including a dismissal of a case.