Poachers will use asny weapon to poach with and the only consideration of choice . . .if indeed there is any consideration is "will using this particular weapon get me caught"? I'm not a crossbow hunter and prolly never will be because at least for right now it just does'nt appeal to me. However if I were a poacher , I don't think a crossbow would be my choice for several reasons including trying to shoot the thing out of a window, possibly having to track him at night in an area that most likely I'm not supposed to be.
From what I've seen most poachers will use a shotgun or rifle late at night, way of out in the boondocks, and hope for the best. Plus, it's mighty popular to hunt the moon with a high powered rifle with a good light gathering scope.

Basically, to be honest the biggest reason most bow hunters IMO speak out against the crossbow is because it represents more competition in the woods in an otherwise low competition season. I know that if it came down to a vote on my part in my state, that would be the only incentive I would have to vote against their use. . . .but it won't, and I don't let it bother me.