[ghaff]

>What's the rationale for not allowing business travel but allowing the same people to travel for tourism?

Many countries don't draw the distinction at least for people with the right passport. But to the degree there's a real rationale (beyond possibly charging more for a business visa and red tape), it's probably something along the lines of the boundaries between routine business travel in another country and working in that country are blurrier than in the case of tourism and therefore some countries think it should attract more scrutiny.

You're right that I could (and have) attended tech events on my own time and my own dime and that seems like tourism by any reasonable definition but does that fact that I didn't take vacation time and maybe submitted an expense report really fundamentally change that?