The marriage between James and Lily was a love marriage. The Potter family had long believed that pure-blood and half-blood wizards and witches were superior to all else and that the world should somehow be purged of all muggle-borns, squibs, and part-humans. Lily’s parents permitted her to marry James. James’s parents permitted him to marry Lily.
The Potter family are just as evil as Voldemort so that they follow in his exact footsteps of attempted planetary domination, overthrow and kill him, and conquer the United Kingdom for themselves. From there, the Potters conspire to take over the rest of the world.
When James married Lily, James was a young innocent man. At the time, James was the only member by blood of the Potter family who were not convinced that to be a Potter made you practically royal with their mania on the supremacy of purebloods and half-bloods and their infatuation with the Dark Arts. Every summer, James took himself, his wife, and their son to their beach house on the Isle of Wight. At summer, James’s muscularity was at its peak; to Lily’s delight as it meant her husband was a bulky and brainy hulk on the beach and to Harry’s dread as it meant his father giving him super powerful noogies.
As time passed on however, it seemed that James deteriorated into the evil ways of his family by when Harry is ten years old. When Lily married James, James was younger and less cruel than he was now so James was not evil at the time for Lily to know him to be capable of becoming what he was now.