As a big proponent of the 2A and generally in favor of less restrictions, I also don't see the point. Here are the times I'd need ammo:

• at the range - just call someone over and they'll deliver it to you
• before going hunting - I'm heading to the hunting store anyway, I'll just pick some up there
• a trip to BLM land to go shooting - pull from stash and refresh it w/ an online order
• when picking up a new gun - gun stores tend to have ammo

Vending machines tend to be in more urban environments, and if I'm there, I either already have ammo (if I'm carrying concealed) or I'm not carrying a firearm anyway. In the rare situation where I'm carrying a firearm w/o ammo (why?), I'm not going to stop and load my gun in public, so why go to the vending machine?

I don't see any good reason for this to exist. Either order online or pick up along w/ other stuff at the gun store. A vending machine is going to be out of whatever caliber I want anyway and they'll probably get restocked rarely, so even a mild convenience would likely end up being an inconvenience. So even if it was safe, it's not solving any problems.

As someone w/ young kids, I definitely don't want to make access to ammo easier for casual gun owners. Gun enthusiasts already know where to get ammo, this is just going to be a target for bored kids.