Not parasites! The REAL reason is in a book very few read or they would know!

Rom 1:18  For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;  Rom 1:19  Because that which may be known of God is manifest in them; for God hath shewed it unto them.  Rom 1:20  For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:  Rom 1:21  Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.  Rom 1:22  Professing themselves to be wise, they became fools,  Rom 1:23  And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things.  Rom 1:24  Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves:  Rom 1:25  Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.  Rom 1:26  For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:  Rom 1:27  And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.  Rom 1:28  And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient;