Personally, my problem with being spied on[1] for commercial purposes is very simple: I object to being spied on. Whether or not there are benefits is irrelevant. The issue is entirely around the lack of consent involved.
[1] I define "spying" as any data collection about me, my machines, or my use of my machines without my explicit informed consent.
[1] I define "spying" as any data collection about me, my machines, or my use of my machines without my explicit informed consent.