The problem with waiting AFAIK is that it's vulnerable to attacks on the underlying peer-to-peer network.
Let's say you wait 1 hour to see whether there was a double spend. If an attacker wanted to, they could spend twice and somehow mess with the network for 1 hour.
For example, an attacker at the internet service provider could intercept packets from the Bitcoin network and just block the other spend transaction from getting to you. You wait 1 hour and consider the payment finalized, and you swap goods for Bitcoin.
Let's say you wait 1 hour to see whether there was a double spend. If an attacker wanted to, they could spend twice and somehow mess with the network for 1 hour.
For example, an attacker at the internet service provider could intercept packets from the Bitcoin network and just block the other spend transaction from getting to you. You wait 1 hour and consider the payment finalized, and you swap goods for Bitcoin.