Is the world flat just because I think it is?
Is the moon composed of green cheese just because I think it is?
Will eating watermelon seeds give me appendicitis just because I think it will?
Can the Great Wall of China can be seen from the moon just because I think it can?
Will fortune cookies determine what happens to me just because I think they will?
The answer to each of the above questions is no. Thinking something is real or right does not necessarily make it real or right. While philosophical concepts can be debated ad infinitum, objective, scientific facts are facts. It can be conclusively verified that the world is not flat and that the moon is not composed of green cheese. A person can be willing to die for their beliefs to the contrary, but that person would still die wrong.
A whole lot of facts can be verified as truth by the scientific method. (If not familiar with its six steps, Google will help you.) A mentally deranged person can scream and spit and kick to support his claim that two plus two equals five. But if you put two apples next to two other apples and then count them, it’s a sure bet you’ll come up with four.
How does one deal with another person who counts four apples side by side and persists in claiming there are five of them there? To begin with is a recognition that something is wrong with that person’s mental or intellectual abilities . . . low IQ or brain damage or brainwashed or some other cognitive malady. Such a person is still to be valued and cared for as a human being, but living in some mental space other than reality necessitates consequences. One who steadfastly denies the Holocaust should not be teaching high school students. One who fanatically embraces authoritarian neo-fascism should not be elected to office in a democracy. Etcetera.
There is not such a thing as an alternative fact. There is fact and there is falsehood. Since most people (I hope) want to base decisions and actions on truth rather than fiction, it behooves one to do serious, responsible homework in the quest to determine what really, really is the truth.