I can see your point of view but I wouldn't be that harsh on those who don't ask permission to record online sessions. After all, these are lessons they pay for. Presumably, they can use lesson notes and stuff used in class. Why not recordings? That's probably the main thing that makes us (teachers) different from many good books. I always encourage my students to record our conversations while teaching online. Being able to listen to the way you speak over and over again is the best way to improve your students' listening and speaking skills. Isn't it wonderful to see them making good progress and realise it is partly your voice that's done it? :)) 

I don't see anything bad in that. I would not care.
Besides, that is not a crime, you can record a private conversation whenever you want but what is important is that you cannot use that recording as a proof at trial for example.

@ Dong-ho Lee - You shouldn't be discouraged, as you can see, this is a fairly polarizing issue. In my opinion you did nothing wrong, and you definitely shouldn't have been made to feel like a criminal. Also, from a legal standpoint, it's highly unlikely you did anything wrong.

mondaytuesday: I think you're right and that they should have asked for a permission first, but may I ask if you would choose to give that permission when asked for? because after all it's an educational session and the learner might need to go over it again and again to study and revise.

I wouldn't mind, but I'd love to know in advance so I can put a nice t-shirt, a gel and look good! ;)