No, you are not allowed (which is the correct spelling) to believe anything you want to believe. You cannot believe you are a police officer if you are not, for just one example. Believing something that counters something so - in your words - scientifically impossible SHOULD be a self-evident proof of mental illness and the only 'proof' we need to lock you away until you are no longer mentally ill.
Short of that, I do get to heap scorn, ridicule and derision on you should you give anyone else crap for 'denying the science' if you believe or espouse to believe there are more than two genders.
THAT is what I believe.