Two example of why it's not.

In 1998 Canada tried to shoot down a weather balloon, it took 1000 rounds of ammunition and 6 days to do it.

During WW1 zeppelins were extremely difficult to shoot down using machine guns as they only made small holes that didn't leak much gas. It wasn't until incendiary ammunition was brought in that they could be shot down by planes.

Balloons you are used to tend to be over pressured so burst when a small tear happens (pin prick). Balloons designed to operate at altitudes like that are at an equal pressure with the air around them, so bullets pass through, making small holes that slowly replace the helium with air thus making them heavy and slowly falling.

The missile warhead generates a big pressure and heat wave that disrupts the balloon tearing it apart. Officially they were worried about damage on the ground, in reality they wanted it to land in water and at a spot they could get to quickly so they could recover it.

>it'll go down really fast i believe

Narrator: it won't.

Key on your last two words here.

You obviously believe that you're smarter than the actual military professionals who worked on this problem every one of whom apparently had never seen an actual balloon before. You believe if you had been sent up there on a paraglider with a nail on the end of a stick you could have brought it down for $300. You believe if you could just get your brilliant ideas out there to the People In Charge rather than in Reddit comments the world would run smoothly.

I believe you may be wrong

Bullets don't make it that high due to air resistance. If you point a gun to the sky, the bullets will not surpass 15000 ft or so. You either need an active propulsion or your projectile needs to be shot with extreme velocity like the ones of rail guns for example