As Sidge says above, you asked if he was going to be deployed, he can't/won't tell you/doesn't yet know, as there has only been chat about it, so fobs you off with a flippant comment.
Being deployed is what the RN do all the time, so it wouldn't bother him.
You did not ask about what he would doing once in the Med, and he would not be able to tell you, being bound by the Official Secrets Act and all that (if he told you he would have to kill you), so I fail to see why you are having such a reaction to his comment.
I've been married to an RN Officer for 25 years almost, and I don't know half of what he does, and I have learnt that if a flip comment is made, to stop digging.
They have a dark sense of humour, summed up by 'if you can't take a joke, you shouldn't have joined'.
Don't read into it more than is there, and no, the RN do not have a mindset like that...and you are extrapolating if you think that 30,000+ think like that on the basis of your ex p.