Just think about the terrorist potential here. Buy a $10 party balloon, let it go near a major airport and they'll panic and shut down the airport. That's a lot of havoc for a couple of bucks.
But what do we know, maybe it was an evil terrorist party balloon. You see, the wall just needs to be a little higher to protect that beautiful country from all southern evils.
Sounds like a great way for a drug-runner to proceed - release 1000 balloons across a very large area, and have only one of them carry their payload of drugs (or whatever).
That said, I doubt they even bother with such small-scale trade. The narco-submarines are much higher capacity and now apparently well-built enough to be trans-pacific: https://en.wikipedia.org/wiki/Narco-submarine
Which way are the prevailing winds at altitude over the Ukrainian-Russian border region, anyway?
How have we not blown ourselves up yet?
It's not that we haven't, it's just that we can only observe from those few realities where we didn't.
Most people aren't sadistically malicious, and most security is professional, so random little failures like metalled balloons or reflections off clouds (or the moon) scaring a security system will only blow up to something important (even on the scale of previous paragraph) every decade or so.
Dann singe ich ein Lied für dich
Von 99 Luftballons
Auf ihrem Weg zum ... well, El Paso as it turns out.
the English rewrite of course starts:
You and I in a little toyshop
Buy a bag of balloons with the money we've got
Set them free at the break of dawn
'til one by one, they were gone...
And rather than see the government have egg on face people (probably a majority here) will vote for politicians who promise all sorts of licenses and regulations on balloons because of it and then in 20yr when I complain and remind them that once upon a time every store used to sell balloons with no KYC BS they'll act like I'm some sort of barbarian, screech, wring their hands, clutch their pearls, etc.