I think I find it unethical because it could put people at risk.
Scenario: I'm playing a game with someone over steam, they take a dislike to how I play. My information I have on steam is minimal compared to other websites I'm connected to but have consented certain types of information on that website (Ie; I haven't shared my email address public on steam, but I'm using the same username on another website where I have it published it would be a personal security flaw I would have rather not had exposed)
They come to this subreddit to try and find more about me, then they have all sorts of access to other data about me and could potentially start harassing me on other platforms because you have made it easier for them to do. It has all sorts of implications including stalking etc...
I cited GDPR because it could land you in a legal grey area, and it has implications with OSNIT as well. https://keyfindings.blog/2019/06/11/how-gdpr-effects-osint/
"Summarising the GDPR, the aspects relevant for OSINT work are:
-You need a legal basis for processing personal data; -You need to apply certain principles in the processing of personal data; -The data subject of whom you process personal data has specific rights you need to understand, anticipate and honour. -Understand if you are the data controller or the data processor."
To give this information to someone without consent of the person who posted their data could land you in some legal trouble from what I understand.
GDPR can effect you if you're using a forum full of unconnected users