Happy to share my notes!

A and B seem to be saying similar things. X will make some people happy and does not suggest that it will make others UNhappy.

I also got confused because they both seemed correct, but the answer choice that MOST weakens the argument is the answer choice that introduces a concept that explicitly goes against the idea of making people happy.

If X makes some people happy and others neutral, it is not as strong an idea as X making some people happy and others unhappy. I hope this makes some sense but that's how I worked it out in my head. I got this one wrong though initially so take it with a grain of salt lol!

interested! would love to join :)