Fast transactions is kinda not really a selling point anymore. If it were Fastcoin would be pretty popular considering 8 second blocks. Many sites only need 1 confirm, or even zero confirms. The difficulty of the network allows for great security.
With each new coin launch, exploiters gets another testing ground. How many coins have been 51%ed or DoSed on launch? Not waiting for confirmations is not security, it's a huge liability. Hence my second criteria: Democratisation... or perhaps better put - better decentralisation.
BUt with bitcoin, its a different situation. Its been out 5 years, and has the hardest difficulty, so its not a launch coin. I believe reading there has only been one confirmed event of double spending, but thats about it.