It's my understanding that in order to successfully double spend you need to be able to mine your own block. And shorter block times makes that alot easier to do. So 10 min block time makes it very hard to double spend in bitcoin.
Yeh, a shorter time isn't safer and is easier to be exploited, though many alt coiners don't realise this. The time it takes to process transactions or get confirmations really isnt a problem and is there to safeguard users and strengthen the system.