Suggest you read
this.
It covers the ground pretty well. This subject has been debated to death. Basically, don't join the RAF if you see it as a cheap way to get an ATPL. The bottom line is that, if the circumstances call for it, you have to be prepared to fight and die for your country. A bit like the Royal Navy and the Army, in fact. The fact that they use aeroplanes shouldn't blind you to the RAF's primary purpose.
But if you're the right kind of guy, it's a great life and a hell of a sight more fun that airline flying.