Sin is pleasurable, albeit for a season. That is why people do it. And people are part of the "darkside" by sin: themselves being darkness. No need to “fall” into it.
But as with all things, there is a price to pay. And there is no safety in numbers: for each person is personally liable for the price of his sin: and that liability is without limitation. Neither in degree nor in duration.
And as it is appointed unto men once to die, but after this the judgment: And whosoever was not found written in the book of life was cast into the lake of fire.
Hence the need to have your sins forgiven.