I'm with the 'just put a brake on it' crowd. The question is, what does it hurt? If it offends your sense of cool, that's not a good reason. The extra 50 grams aren't much of a concern when you're just commuting. It won't hurt the performance of the bike at all.

To offer one suggestion - not only would I put it on, but use it a few times every time you take it out, for a couple of reasons:

1) you don't want gunk to build up on the pads and rims that could impair the performance of the brakes, and
2) you want to be used to how much pressure on the brake generates the necessary deceleration. Since you only plan to use it for 'panic' braking, you'd have a good chance of doing an endo if you don't practice it.