They might want to require more then one confirmation for large withdrawals however they should not accept no confirmations to bet.
The only site that I know of that accepts 0/unconfirmed deposits that takes successful countermeasures against double spend attacks is 999dice, however I understand they are also separately a scam site.
There's really no fool-proof way to accept 0 confirmation transactions that I know of. Services like bitpay/coinbase must run some sort of quick analysis to determine the risk of the transaction being a double-spend based off certain factors like fee, inputs, etc. I think 1 confirmation is pretty reasonable and shouldn't be a major inconvenience to anyone (8-9min wait generally), we're always looking into ways to improve user experience though and will do some more research into this.
Also, someone else registered the name 'stunna' on the bitcoin.com forums. Just letting you know that is not me. I'm still getting messages regarding people impersonating me on other sites/chats as well, stay safe.