Halo combat is a lot about map control. Controlling the power weapon spawns is a big deal. Controlling the laser is a big deal when vehicles are on a map. If everyone could spawn with a laser, vehicle combat becomes obsolete. Not only that, but the laser kills infantry quite easily as well.
Not saying that they will not have weapon unlocks or something along those lines. But it would most likely be a large divergence from the normal Halo combat experience.