Ah you got me, though I don't think it changes that much.
Even with an online 'form' (presumably a phishing page) I don't understand why anyone would ever upload private keys for their wallets.
In the case of exchanges, users typically don't get access to the private key for the wallets anyway, so pretending to be an exchange to phish for something the victim can't even provide wouldn't make sense.
In the case of a local wallet, the whole purpose is personal ownership of the coins—which obviously becomes moot when sending the private key to some random person—so I don't see why a user would upload them in this circumstance either.
Though yes, the situation is certainly more understandable than GP posting private keys to an online 'forum' ;)
There's overwhelming empirical and anecdata evidence people make mistakes and fall for phishing. If that doesn't change your mind that much, it's not obvious what reasonably could.
Sorry, why would you ever disclose your private key to some online forum? I can't see a situation where it makes sense.
Clearly there's something I'm not thinking of, so I'm genuinely curious