Maty Ezraty's reply:
This is an ethics question and has no black-and-white answer as far as I am concerned. It depends on the situation. Personally, I do not object if a student looks at yoga class as a place to meet people. Humans expect to meet like-minded people in environments they enjoy.
But there is a line that should not be crossed. One student should never behave in ways that cause another to feel discomfort. In a yoga class, students should not dress inappropriately or send unwelcome vibrations to others in the room.
When behavior becomes inappropriate, it is the school's responsibility to intervene. If you sense a problem, ask a school administrator to talk to the student discreetly. (I've found it is better that the teacher not talk to the student directly—that way the student is not embarrassed to return to class and study with the teacher.) Sometimes people are not aware of their actions, and a gentle approach may help them realize how they are being perceived. It is best if they can see what they are causing, choose to fix it, and remain yoga students. Then you have truly helped.
Lastly, it is important for the teacher to hold to this sacred commitment and not cross the line and date students. Teachers, after all, set the example.