There are sometimes that you wonder how people can derive such different conclusions simply through different small biases they may encounter early in their lives. I grew up in a conservative household and listened to conservative media for years and all of it seemed normal and believable to me. Had I been a little less critical and skeptical of politicians, I might have been of those buffoons yelling MAGA! and wearing those stupid red baseball caps. But not everyone is fortunate enough to escape the realities created by their exposures to particular biases.
Belief is an interesting thing. Beliefs are more powerful than truths and people follow their beliefs and not necessary the truth. But sometimes people belief things that simply aren't true. But then again, within the previous statement, I am imposing my own beliefs without any indication of truth behind it. You might have evidence to suggest the same, but such empty statements are certainly not convincing to all people.
But let us explore the question rather than jump through logical hoops as fun and interesting that may be. First let us define some terms in a way we can all agree with. Reality is the real part of the universe. It encapsulates everything that truly exists. Subjectivity means that viewpoint is made from a personal perspective.
Given the knowledge we have, we can actually reach an answer pretty easily. The answer is that reality is not subjective. Since it is everything that truly exists, it is independent of any viewpoint applied to it. Thus, the reality we all share is universal and objective. But our lens of such reality are shaded by our perspective. The issue is that the reality we perceive and the reality that actually exists can be two completely different things with some overlap.
Of course, you could reject my definitions and argue for the opposite conclusion which in itself would be interesting, but let's focus on a more important question:
How do we discover reality?
For most of us, we simply gather evidence and use that evidence to shape our beliefs. Ideally, we would like for these beliefs to be reflective of reality but unfortunately due to limited perspective, we will always have only a portion of the picture and we will have evidence that isn't necessarily conclusive.
You see, two parties can be given the same evidence and draw different conclusions. Depending on different biases and beliefs, one person may emphasize certain evidence to claim A is true, while another person may emphasize other evidence to claim the opposite is true. And there is no way of telling if claim A or claim not A is actually true.
There are people who appear to make ridiculous claims but believe their side of the story is the true. This is because they use different evidence and view that evidence differently. Some things may appear credible to an individual and yet are rejected by society as a whole. And it is hard to tell who is right, even though it may first appear that the person is a raving lunatic.
The environment may make certain people more vulnerable to believing conspiracy theories. They will tend to believe certain pieces of evidence that support such theories and will analyze that evidence in such a way that it supports their theory more strongly. And thus, you have people who believe things that may appear to be crazy or illogical. But you can't really show them that they are wrong.
Because you only have a subjective view of reality like they do. You only pick parts of evidence that support your beliefs and arrange that evidence to strength your beliefs. You do the same thing, but have developed such ideas within different environments and thus have different biases to lean in certain directions. The challenge is to acknowledge these leanings and understand the potential jumps in logic we may make to reach certain conclusions we may be primed to accept.
We'll never be able to definitely declare statements rooted in absolute truth, but only subjective representations of the real thing that may be significantly warped. There's nothing much else to say other than humans are fallible beings and we should stop being stubborn assholes all of the time.