Why doesn't he just grab forty or fifty of the Lilliputians and kill them?

Gulliver didn't want to be pelted with hundreds of arrows.

Whereupon I once more thought of attempting to break my bonds; but again, when I felt the smart of their arrows upon my face and hands, which were all in blisters, and many of the darts still sticking in them, and observing likewise that the number of my enemies increased, I gave tokens to let them know that they might do with me what they pleased.