To OP: It really depends on how much time you want to invest in talking to a particular person. If they are close personal relatives, it may be worth taking the trouble, and gently explaining your position. Otherwise, it's not really worth it, unless you relish the entertainment factor.
I find it helpful to compare the current anti vaccine/Big Pharma/anti GMO/chiro/naturopath fervor to previous examples of moral panic that have risen and fallen in the public consciousness over the past decades, like playing Dungeons and Dragons leading to Satanic baby sacrifice, or the seemingly pervasive rate of alien abduction in the 1990s. If you look back on these, the distribution of belief is pretty similar: There was a core group of true believers that found signs everywhere, and pieced together disparate "evidence" to make themselves irrationally fearful and angry, there were stories featured in media that appealed to emotion (from silly tabloids to Reader's Digest), and a large segment of middle America that credulously entertained the ideas.
Neither of these two things are really in the public consciousness today.
So what happened? Did the Dark Lord become satisfied with the blood of infants, and not need to manipulate nerdy teenage minions to do his bidding? Did the aliens fill their quotas? Did the flying saucers become too heavy with all the kidnapped bodies?
Or did the credulous portion of our society lose interest?
All of these things involve some amorphous evil entity, vague reports of unfortunate events, and enough public interest to keep generating and perpetuating them. After a while, it just sort of becomes obvious that a lot of people played RPGs, and the thought of kidnapping babies just never came up. One could drive down empty back roads in Nebraska, go camping, and have no fear of being probed by aliens. Similarly, most of us have been vaccinated, eat some sort of GMOs in some sense, and are COMPLETELY healthy, and do not need a "vaccine/toxin detox diet" or spinal adjustment to restore our vitality.
The key to not alienating people that you actually like is to point out that all kinds of perfectly intelligent and otherwise rational people fall subject to misconception and irrational thinking at some point in time. Linus Pauling, for all his genius, was fixated on Vitamin C, which has never really proven to be as widely beneficial as he thought. I have met very intelligent high performing people in medicine, who for a brief moment, were taken in by the chemtrail hoax. It happens to all of us at some point in time.
For people I don't like, I prefer to one up their pseudoscience: After all, why should I be concerned about Big Pharma and GMOs when the Annunaki have been dominating humanity since the dawn of time? Don't believe me? You should educate yourself. There are (frankly quite awesome) Youtube videos detailing the archeological and anthropological evidence of this. It's all there.