Wishful thinking should not be confused with positive thinking, which, in its most absurd form is a kind of magical thinking that involves trying to make things happen by willing them to happen. In its best form, positive thinking is hopeful and optimistic, but realistic.
Wishful thinking sometimes evolves into motivated reasoning, which not only interprets data according to preferences but actually takes disconfirming data and turns it into confirming data.
Motivated reasoning is a major obstacle for rational argument. If someone wants to believe that asylum seekers are breaking the law, or if someone wants to believe that virtually all of the world’s climate scientists have conspired to make up a huge global “climate change hoax”, then it is very difficult to change their minds even when the actual evidence is very, very clear.*When confronted with someone whose belief system seems to be built mainly on wishful thinking perhaps the best one can do is provide alternative interpretation(s) of the data without insisting that the believed interpretation is wrong. Direct challenges to such a belief system may backfire. Actually, even the mere suggestion that valuing personal experience over scientific facts and probabilities might be harmful to your health is often met with self-serving dismissal.