Being able to "handle that weapon" and being able to proactively and effectively engage an active shooter 65 yards away while offering minimum danger to innocents are two different things.

I think the comment you have an issue with is entirely appropriate to the discussion.

Furthermore, how do you know there was only the one armed citizen in the area. There could've been 10...or 100...armed people in the area who chose not to intervene and who've chosen to remain silent for various reasons.

Arming yourself to protect self and loved ones only is just as valid a reason to carry as any other. I have no legal obligation to protect anyone. The moral obligation I feel to protect (or not to protect) society in general is my business alone.