These days I find myself missing those tough questions, not because I enjoy confrontation per se, but because they made an important contribution to my education.
To be clear, bullying questions or competitive questioning meant to highlight the questioner’s intelligence are a waste of time (e.g. two minutes of talking about your research followed by "what do you think about that?"). Critical thinking, while one of the most important aspects of a post-graduate education, can't be taught. But tough questions and questioners model critical thinking for students in the most direct way. Being at the front of the room talking does not automatically grant expert status: the speaker's ideas must be clear and robust to debate.
Difficult questions benefit a speaker too - they are the clearest demonstration that the audience has engaged with their work. The most useful talks are those in which the questions are thought provoking for both the speaker and the audience.
And finally, it can be refreshing when a questioner holds a person to actually answering the question. Science is built on debate and some times disagreement. Hard questions made me feel that the people asking them were expressing a preference for good science, even if the cost was some discomfort or social unease. And that feels like an important thing to express.