I think "all or nothing" is a difficult position to sustain, whether it's medicine, chiropractic, acupuncture, nutrition, this diet or that diet (carbs/no carbs, sugar/no sugar, etc.) and so on.
I think your PCP's info is incomplete - my understanding of the "stroke" problem is that, with a lot of cracking of the neck, some patients (particularly the elderly and others with a large plaque build-up in the arteries), some plaque could be dislodged and cause a clot, which could cause a stroke. That's why a lot of practitioners don't do the cracking (which some call "Pop And Pray"), but do more gentle manipulation such as applied kinesiology. So you might look into that. Lots of MDs do refer patients to chiropractors, so your PCP's feelings aren't universal. In that regard, your chiropractor is correct that there wouldn't be a single practicing DC left.
Many chiropractors approach their practices with the idea that they deal in acute care, but that visits should taper off. I went to one who very clearly stated that, if I didn't have significant and measurable results in about 6 visits, then HE was doing something wrong. Maybe not a complete cure, but a big change. Now, you can argue the 6 visits vs. 4 vs. 10, but the idea is the same. But the same might be said of MDs - I had one doctor who did ridiculous tests to either drive up the cost (like an EKG every visit even though I had no heart problems, and a breast exam every visit which I thought was just abusive and ethically questionable and for which I reported him). So you can't throw out an entire field of study or practice because there are poor practitioners.
I'm with you on the vaccine issue. I think there's no excuse for this guy saying he won't vaccinate his kids - so they are at risk and they are exposing other people to diseases that were largely horrible for all who got them (measles, mumps, German measles, chicken pox, polio). I think you can argue the flu vaccine because there are so many strains and it doesn't seem to provide the protection that the other ones do. But the return of these epidemics because of a lack of belief in research is ridiculous.
That said, you don't have to agree with every single thing a practitioner says, in any field. No, a chiropractor didn't go to medical school, but your MD didn't go to chiropractic school or pharmacy school or massage school or physical therapy training, and many of these practitioners rely on each other for expertise and help. My mother broke her shoulder, and she needed coordinated services from an orthopedic surgeon, an Xray technician, surgical nurses, rehab physicians, rehab nurses, physical therapists, occupational therapists, social workers, personal care attendants, and home aides. Nobody said, "Don't listen to X or Y because that person didn't go to medical school."
I think the question for you is, are you getting benefit? Maybe you don't need to go every month, maybe you do. There's only one way to find out. But the same could be said of "maintenance medications" - I was told I needed to be on 3 different ones, but now I am off them and maintaining my health through a combination of other regimens. One PCP was very pro-medication and convinced me I had had a "silent heart attack" among other problems, but a cardiologist told me my bad EKG was based on faulty wiring in the leads (great - bad equipment). Another PCP in the same practice was thrilled with my improved lab results and positive changes (reduced breast cysts, better cholesterol, etc.) using supplements, and she told me to keep at it because she couldn't argue with success plus clinical trials. But it depends on the person, the medication, and other factors in the person's life and immune system. You might do well, for example, with a natural anti-inflammatory, some sort of exercise (yoga, strength training, stretching), and maybe fewer visits per year.
So it sounds like both your PCP and your DC are scared of the worst possible scenario. The PCP is afraid to endorse anything that might cause a stroke (whether or not there is evidence of that and without knowing what method your DC uses), but he doesn't know anything about chiropractic. Your DC is freaked out about the vaccine scare stories, but he has no info on real clinical data and didn't go to med school. Other doctors are scared to death of things like statin drugs, while others swear by them because they don't want to get sued by someone who died of high cholesterol. Some of them will look into alternatives like natural peptides from plants, some won't because they are either not open, not up on data, or afraid to endorse something outside the area covered by their malpractice insurance.
So I don't think you can look at any one practitioner as the expert on all things. You are the ultimate decision maker on your body.