It's true that there are somethings that we just can't be certain of. But there are things that we know to be true and yet steer into the "grey" to avoid following Jesus.
Such was the case when it came to the question of divorce. When you boil it down, the debate wasn't really about divorce. It was about who follows who. They wanted Jesus to come follow them into the "grey." Jesus' answer however challenges them to follow God into the clarity of his original intention. Listen to his words:
“Because of your hardness of heart he wrote you this commandment. But from the beginning of creation, ‘God made them male and female.’ ‘Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.’ So they are no longer two but one flesh. What therefore God has joined together, let not man separate.”
The Pharisees read Moses' words about divorce (Deut 24:1-4) as a pre-text for divorce when it's original intent was really to limit divorce. Divorce was a concession - never God's original intention. Such is the case with many things in our life. Following Jesus is more often not a question of choosing between right and wrong, but between what's permissible and what's perfect.