a. closing one attack vector does not justify slowing down the entire world. b. you can have the jit compile with any bound checks as you suggested, so still not justifying an interpreter. the only reason for an interpreter is simplicity, once you have a jit there's no logical reason to go back. also when you say NX bit, you do know the interpreter is running code still. it's just doesn't have to be RW (actually jit don't either) which still allows for ROP. there has to be some very specific exploit for these things to have a dramatic effect (ie. can be vs. cannot be exploited) many times there will be several methods to exploit a vuln.