In this case it's not disagreement with one expert, or even a few. The vaccination schedule is based on a consensus of experts. Not only across organizations, like the CDC, AAP, FDA, but across nations too, more or less.

It's truly bizarre to _radically_ disagree, especially as a layperson.

I mostly share your assessment, except that I think the word "bizarre" presumes how normal people behave. These kinds of attitudes have been around since at least the Spanish Flu pandemic, so it's important to… how do I phrase this? To account for such attitudes when planning public health campaigns, and not just dismiss such people as arrogant fools with no self-awareness.