The problem is that Trump and his minions do not have the intellectual capacity to distinguish between truth and lies or facts and falsehoods because their brains suppress all facts that disagree with their ideology. 
Climate change is is a small example. They disregard the findings of the 97% of peer-reviewed studies that state  that climate change is real and caused by the actions of humans, preferring to believe that the 3% who deny the evidence are correct.  Trying to claim that Trump's crowd at the inauguration was bigger, despite the visual evidence that clearly showed it wasn't, is another example. 
Alternative facts, as they call them, are not facts. They are lies, pure and simple, and they must be called what they are.