The Bible does not teach that angels did have or can have sexual intercourse with humans. One particular reference comes from Jesus teaching that there is no marriage in heaven, but we will be like the angels. (Matthew 22)
As far as evil, Satan surely fits that description. But humans have a heart that is deceitful and desperately wicked and capable of much evil. (Jeremiah 17) Our own heart is the major source of temptation. (James 1)
In the days of Noah, disobedient angels did take on human form. (Genesis 6:4). "In those days, and even afterwards, when the evil brings from the spirit world were sexually involved with human women, their children became giants, of whom so many legends are told." (Living Bible) When the flood came, those angels were forced back into the spirit realm. Regarding them Jude 6: "And the angels that did not keep their own position but left their proper dwelling have been kept by him in eternal chains in the neither gloom until judgement of the great day. (Revised Standard Bible. "And the Dragon lost the battle and was forced from heaven. This great Dragon---the ancient serpent called the devil, or Satan, the one deceiving the whole WORLD---was thrown down onto the earth with all his army." ( Revelation 12:8-9) Living Bible. Believing that Satan exists does not mean accepting the idea that he has horns, a pointed tail, and a pitchfork. That is a product of medieval artists who were influenced by representations of the mythological Greek god Pan and by the Inferno written by the Italian poet Dante. Point is that the Devil does exist. Again reference to the Bible " the world around us is under SATAN'S power and control" ( 1 John 5:19) Living Bible. And again this is not my personnel thought, this is what the Bible says. People can choose to believe it or not. Please don't kill the messanger.