So how precisely do you distinguish the two. Becasue it seems to me like many, many of the complaints of "stalking and harassment" are just people hearing comments and communication with which they don't agree.

Real stalking or harassment is a crime. If its actual stalking or harassment, the police should be involved. What many on the platform are concerned with is "he said something to me that i dont want to hear" but they know they won't get support to stop that, so they use criminal terminology to discuss it.