Why point the whole plane at the target. Why not moveable forward guns?

[Bearcat]

In a nutshell.. That might have worked in WWI .. might have.. but can you imagine trying to fly and aim a gun.. at least with fixed guns that took out one step.. just put the plane where it needed to be and shoot.. Also.. I imagine that aimable guns would wreck havoc on flight attitude.. as it was when a P-47 fired all it's guns there was a noticeable drop in air speed.