Isn't it dangerous to give out your bank account number in the US, people can withdraw from it if they know it or something?

You'd also need the routing number for the bank as well as the name on the account, at a minimum. And what you're thinking of is ACH, which goes between institutions, not between individuals.

The routing and account numbers are on all paper checks you write. You can use them to set up ACH transfers to/from that account, with pretty minimal checks.

Those transfers have to go through heavily regulated institutions, however, all of whom have strict KYC laws. Of all the ways to try and steal someone's money, this would be fairly low on my list.

USA doesn't even have a standard way of normal humans transferring money electronically to each other, leading to a plethora of competing apps that try to solve this.

The US has a couple of ways that normal humans can transfer money electronically to each other. But they're old school (and require bank accounts) and that's why there are newer systems that people use instead.

There are upsides and downsides. Having an additional degree of separation is nice when I'm doing transactions with strangers. I prefer to use Venmo instead of Zelle for precisely that reason.