If you do hydroponics then that's less of an issue. Most of the bugs need the soil. And the ones that don't can be dealt with by hitting them with some safe pesticides.
I would disagree. The only greenhouse pests that need soil are fungus gnats and thrips. Fungus gnats can be taken care of by drying out the soil but even when left to run amok don't really cause serious damage. Thrips need to be killed though.
Meanwhile aphids, spider mites, broad mites and whitefly don't need any soil at all and they can cause some serious damage right quick. Good luck taking down most of them with "safe pesticides." Don't get me wrong, most of them can be handled safely but I wouldn't want them near my food at all.