Why not? It's a bit direct and perhaps odd and unexpected, but also polite, possibly flattering, and a very decent way of taking a chance on getting to know someone who you will likely not meet again unless you take action, better. If the response to the rejection of that offer is polite and professional, then how is this inappropriate?

As one of the people he asked out mentioned, his response to the rejection was anything but appropriate (he threatened to kill himself) [0].

0. https://medium.com/@selamie/remove-richard-stallman-appendix...

It’s appropriate at a bar. It’s not appropriate at a professional conference or at work. Especially with the age / seniority difference, this is textbook sexual harassment.

> this is textbook sexual harassment

Saying that doesn't make it so, you have to actually back your claim up with some reasoning.

Fair enough, but that knife cuts both ways. Explain how it is not.

Explain why any young woman in tech would want to go to a conference where a bunch of old guys think it’s perfectly ok to treat her like a potential mate, instead of a colleague with a brain and technical background worth learning from and mentoring.

Explain why she should have to put up with shit like this, while her male peers do not.