Unless the professor has specifically set aside time for questions or random 1L expounding, its not appropriate. A gunner is someone who interrupts class to ask some inane hypothetical or make some inane comment. IT DETRACTS FROM THE CLASS AND HARMS OTHER'S UNDERSTANDING. Usually the prof is trying to get to some point or is purposely leading things a certain way and when some jackass raises his hand to offer his hypothetical or ask some unrelated question or just keeps the prof from getting to the point it ruins the f'ing class for everyone else.
If you have a question or comment that has not been specifically solicited by the professor, save it for office hours.
Usually professors are open to people asking questions. In fact, they build time for it into their lectures. Further, good professors tend to love going off into diversions that are related to the main point, because they actually like what they teach. Part of the art of being a professor is "bringing it all back home." Learning law isn't a highway, there are a lot of detours. It's not like we're marching through the periodic table, and people interrupt to talk about phlogiston!
I agree with you with respect to utter irrelevance, but I feel like the attitude you are expounding shuts down fun and relevant class discussions.
I assume we're actually pretty much in agreement, because I agree that people shouldn't keep distracting professors with irrelevancies when they're trying to get their points out. Different professors do things differently, though. Also, I tend to assume professors are capable of cutting people off if they don't want them speaking.