If it’d cost less than say 2x what it’d save, I’d say it’s beneficial. Making it obvious that corruption isn’t going to work has value, but no need to do really extensive audits just to get the last 0.1% of mistakes/fraud.

By the time they’re going fast enough, they’re high enough they don’t have much air to worry about. (And they do have an angle over too, not just straight up)

Missiles do go more or less go straight though the atmosphere horizontally. Most are slower than what we’re taking about, but hypersonic missiles get close to rocket speeds. And they do need big heat shields to keep from melting immediately.

You’re going much too fast to hit the earth, you’ll miss it and continue in orbit. To deorbit, you’ll need a lot of things to throw in the other direction, like the oxygen from your magic tank. You’d need about a full rocket full of oxygen (~170 tons) to slow down, probably more because the exit velocity would be slower than a rocket.

The other issue with this scheme is you’d slow down too slowly. You’ll start getting slower and lower, but you’d start to get into the atmosphere, which because you’re still going so fast would cause you to not have a great time. So your magic oxygen bottle will also need a massive tube off the end of it, maybe a couple meters in diameter.

But if you had your magic infinite air tank with a huge tube off it, theoretically you could get back down to earth safely with just it, a space suit, and a parachute.