Stupid questions exist. There is the occasional student who often asks those. Do not be that student!
Fortunately, most questions are not stupid. For most questions, a significant, silent fraction of the class appreciates that the question is asked. (How do I know? Several ways. For instance, when a question requires a long answer, before answering, I will sometimes gauge interest by inviting all interested students to show their hands. More often than not, several students will want the answer.)
Also, if the instructor is teaching the course in question for the first time, sometimes students who are not otherwise troublemakers ask questions merely to slow the lecture down, because the lecturer is inadvertently covering too much material too fast. Such questions represent valuable feedback.
Occasionally you get a student who just probably isn't smart enough to pass the course. If you politely invite that student to bring his or her questions to office, that student usually gets the hint and stops stalling the lecture with questions his or her classmates don't care about. The student may or may not then come to office, but that's for the student to decide.
The problem student is the student who asks questions because he or she likes attention. Every class of a certain size seems to have one or two of those. The classmates usually don't like that student, either.
All you can do with a student who asks questions because he or she likes attention is (a) call on other students first whenever possible, (b) give the troublemaker curt answers and smoothly move on with the lecture without inviting further discussion, or (c) in the final need, affect for a while not to see the student's raised hand. Unfortunately, most such students won't take the hint. Oh, well.
Fortunately, most questions asked are worth answering, or at least worth respectful deferral, in my experience. Moreover, depending on an instructor's lecturing style, good questions (which often arise) really help a lecture to move along. Some of the best questions come when the instructor has briefly glanced upon some point the instructor thinks is obvious but the students don't. The instructor needs to know that.