I had to go look up who this was so I could decide if I was outraged. My take:
1) It seems he may have inadvertently killed someone who may, or may not, have posed a direct threat to him.
2) I have no idea what second degree manslaughter charges mean in NY, nor am I taking the time to look, but I suspect the evidence either will, or will not support the charge(s)
3) Guy was in a tough spot. It is a fine line between dude is having a mental break, threatening harm and is really gonna do harm vs dude is having a mental break, threatening harm and is really harmless. I don't know how you decide.
4) This kind of thing makes it more likely that the next guy who is thinking about stepping in and "helping" might just sit there until harm is done, and possibly severe harm.
5) Given all this and limited knowledge of facts beyond some biased headlines, I have no idea what constitutes "right" or legal in this case.
6) The whole thing sux start to finish; no matter how it turns out for this dude