I'm not sure if there's a conscious choice to ignore logic, or if it's solely based on mistrust and paranoia?
Hanlon's razor guides us to
Never attribute to malice that which is adequately explained by stupidity.
Now I don't really think anti-vaxxers are stupid as such, at least, not all of them. I think it's unproductive to make that assertion. Some people might say I'm stupid for believing some of the things I do, but I'd rather they didn't, and I believe in treating others how I'd like to be treated.
I also don't think they're purposefully ignoring logic. Instead, they are driven by paranoia and distrust into a sort of self-perpetuated skepticism of life, the universe, and everything. Just as vaccines give us herd immunity, anti-vaxxers share amongst themselves a sort of herd ignorance. It's involuntary.
We can prove vaccines work. We have data to support it and a widespread, decentralised, and organic web of trust confirms it. But something happened with these folks' lives which shook their faith in that web of trust, or did not allow it to establish in the first place. If you are raised believing not to trust the establishment-- as part of a "chosen people"-type religious sect, for example-- then you won't know any better than to immediately dismiss anything widely regarded as fact simply because it is the mainstream status quo.
Anyone who's ever been religious can understand the cognitive dissonance encountered when considering evidence which contradicts dogma. There's an interesting sort of ever-present nagging feeling that none of this is real. That it's all a test. If you've never been religious, a way to awaken similar feelings within yourself is to consider that you are living inside a simulation. Imagine the skepticism with which you would approach almost every assertion from someone who doesn't share your belief in the simulation. You simply cannot get anywhere in a debate against this sort of reasoning. The only winning move is not to play.
I suspect that internet propagation of urban myths enjoys some infamy in spreading controversy and the idea that you can't believe what you read by supposed authorities (Bill Gates will send you money if you forward this comment to everyone you know. I live in Seattle and he's been sending me checks for years!) and now we have 'fake news' to add to it (After H&M faced huge controversy for putting an African American boy to model a hoodie which read “Coolest monkey in the jungle”, It is being reported that H&M is planning on releasing a new collection that according to chairman Stefan Persson, is “equally racist to all the other races”. The collection will be called the “You’re Not Alone” collection.) Both of these types of things erode our ideas that mass disseminated information can be trusted.
Belief in false info isn't new but now that we have an easy method of checking facts (people don't do it anyway) we also have a wider distribution of falsehoods and for fake facts.
(@suesa!) Pumpernickle, compared to other breads, is actually quite healthy as it has a very low glycemic load (low carb) and contains a boatload of resistant starches (doesn't digest easily and provides fiber) if it is honestly made from pumpernickle flour and isn't cut by white flour.