Yes, overthrowing a dictator is often sufficient cause for terrorism, if the dictator hurts a lot of people. Just not liking a dictator is not a good reason, but if the person is killing or starving his or her own people, it is ok to want to take them out in order to prevent more people from dying.
As bad as dictators can be, when you step over the line of terrorism and lose your humanity, there is no looking back. Suddenly murder seems to be the answer to any problem. Plus, the definition of a good or bad leader is subjective to different nations, and one nation should not be able to tell another that its choices are wrong.