I don't how much 'soft power' Owen was supposed to have 5 years ago (by being older and more involved in the community). While it's regrettable if someone pretended to be comfortable while actually being uncomfortable, it's unclear to me that the perception of 'soft power' would matter so much that one cannot speak up.

I think 'randomly' doesn't apply here. Owen had multiple conversations with the person about 'edgy' things, including sexual things, including masturbation. 

Suppose I have a friend who sometimes talks to me about masturbation, and with whom I sometimes talk to about masturbation. Suppose one day, my friend said that they were uncomfortable all along, I would find that regrettable, but I don't think it's my fault they didn't speak up previously.

Please read my edit carefully. 

If anyone feels that someone's career deserves to be harmed to such an extent because they unintentionally made someone else feel uncomfortable

My argument is that if people continue to push for more absurd demands on other people's behavior ('this person should have known this other person was uncomfortable even though this wasn't communicated to the former person through multiple opportunities during repeated interactions of a similar kind'), those demands are going to critically damage the society they live in.

People naively ignore the fact that if they agree on penalizing people to such an extent for simple mistakes, then it's likely that a reaction from other parts of society (parts that I assume many people here have to little to do with) will cause at least some rollback of the freedoms that were hard-won by more serious activists from the past, as well as prevent progress on many serious efforts that are ongoing today, by being associated with such radicalism.

Also, I think it's simply authoritarian. Let people make mistakes without having to endure this kind of persecution.

Should I add the word "ultimately"?

Very well. "a single comment which led to that other person openly object to that former person's behavior".

You are correct. My mistake.

I'll rephrase that as "If anyone feels that someone's career deserves to be harmed to such an extent because they unintentionally made someone else feel uncomfortable with a single comment, then I think people who hold that opinion should grow up."