I think the confusion here comes from viewing it as a single issue with sides rather than multiple aspects.

It's a crude comparison, but it reminds me of a discussion on Reddit where someone was struggling over whether it was time to put his dog down or not. One poster responded by essentially asking whether the OP liked their dog, and if they did why they would kill it, and then summed up by stating that anyone who could consider euthanizing a dog never loved it in the first place.

I actually like the sentiment if it is talking about a dog that had grown inconvenient, and it was probably expressed by someone who deeply cared about a first dog, but had never had a dog grow old. Of course, there were some pretty irate responses from people who had dealt with the real situation of a dear friend no longer enjoying life and feeling constant pain. Perhaps one of the difficult parts is that even the clearest cases, it is just resigning yourself, since doubts will always remain. It isn't difficult to imagine that you can always induce one more tail wag from your suffering dog, or presumably to imagine a glint in the eye from a loved one. That OP was in search of information to help make a difficult decision, and the only context that was relevant was that particular dog's health, not someone's ideological objection seeking to make it an issues with sides.

Imagine for a second if there were a sides debate over "medication" (of all types). There would be many constituencies lining up on those fakes sides. Some would talk about abuse, and health danger of using too much medication. Some would talk about personal liberty, and that people should be able to take what they want. Then there are some who believe that suffering is intrinsically virtuous, while others believe it is unethical not to treat pain. Some might believe that it is cheating for someone who doesn't exercise to take statins, while another group would argue that as prevention they ultimately save money and increase quality of life. I'm sure the people with eugenicist tendencies would want their say, too. And quite likely all of this would occur without any consensus over the relative importance of making people productive, or lucid, or comfortable, or keeping them alive, because the importance of these goals aren't only personal, but informed to varying degrees by the differences in regional and socioeconomic cultures.

Simply put, there aren't two sides to the vaccinations-and-marijuana issue, because it isn't even one issue in the first place. Is there someone who worries that it is a slippery slope from using general anesthesia in the operating room to vaccinating children? Probably, but you'd have to accept a lot of premises before even being able to engage in such a conversation. While there may be people who are in favor of or against two independent things for a single reason, those reasons are not the reasons that most people care one way or the other about either. Conflating them would be a trick to elevate those frameworks.

Likewise, whether or not to knock off an older person who wants to live but can't pay for their nursing home, isn't the same issue as assisted suicide, which isn't the same as a 'do not resuscitate' order, which isn't the same as decisions about who does or does not get access to a life-saving operation.

Allowing special groups to decide which issues get conflated into a single debate and then turns into two sides is an abdication of the responsibility to think critically on important policy matters.