A caterpillar on your cauliflower is a sign that the cauliflower is safe to eat!
Wash all fruit and vegetables well and discard the outer layers where these may accumulate pesticides. The only way of being sure that your vegetables are free of pesticides is to grow them yourselves, but you will then discover how hard it is to produce the unblemished pest-free produce on the supermarket shelves without the aid of pesticides.
Pesticides are probably more harmful than no pesticides, because many are nerve poisons and can accumulate to dangerous levels in the body over many years. But for many people in the world the choice is to accept a low pesticide residue on their food, or starve to death as a host of pests decimate the worlds crops while they grow, or destroy crops while in storage.