The use of hurtful nicknames in the workplace can indeed be considered harassment in the eyes of the law and/or polite society.
That being said, not sure pronouns are indistinguishable from names. As a species, we evolved sexual dimorphism alongside a visual apparatus to detect the dimorphism. We are able to tell a male from a female at a glance with high accuracy, even in presence of elaborated disguises. Being asked to call someone we perceive as male "her", or someone we perceive as female "him" is often times difficult. The pronoun is not an arbitrary tag detached from perception, visual or linguistic. Picture a couple more situations:
* A 6ft bearded hulking person insisting to be referred as "she".
* A person insisting that their name is "Susan", but that we should refer to them as "he".
Plenty of people would have to make an explicit effort to comply with such requests, beyond what's required for remembering the mere name/pronoun tag.
Online, we interact with a huge number of people, possibly only for a few brief moments. Most of us simply use the name tag under our eyes, and infer the pronouns using linguistic clues. For example, most people would use "he" to refer to u/henrikschroder. For name tags with less obvious genders, most people would default to gender neutral. Taking offense at people using an inferred pronoun when no other information is readily in sight is akin taking offense at HN readers that don't read the linked article before commenting. Nobody has time to click links on the Internet.
As a culture, we'd do well to stop catastrophising and taking offense at people minding their own business and not being hyper-aware of everyone else's special circumstances.