i dont use a lot of it but i have absolutely no reservations about using synthetic materials nor do i look down at tyers who use it
the basic premise of fly tying it to create an imitation of a food source that a fish will eat. whether its done with natural or synthetic materials is irrelevant.
there is no fly tying commandment that states "thou shalt only use natural materials when creating imitations of fish food"
it all boils down to "tyers preference" and nobody should be judged as to what they prefer.