in reply to
In Defense of Perl
Unfortunately, what you have is a religious war on your hands. Many have given excellent business advice on ways to combat it above, but there are also many historical and current computer related religious wars from which you may be able to glean insight from. There's a nice list to be found here.
Any time people argue about any topic, and those people's beliefs are rooted in fundamentally different places, the argument can not be resolved until they are able to find common ground from which to work. Those giving business arguments are hoping that your manager will be swayed by business logic to abandon his attacks. If he stands to lose 'face' by continuing to attack, it is likely that will work, but it isn't guaranteed.
In the end, as evidenced by the prevalence of these 'wars' and the length of time many have been perpetuated, it is often an ugly and protracted battle. Study up on "The Art of War", arm your self well, and my you win the good fight.