People don't in general think that crutches are bad things. But we don't like to see ourselves as cripples. And so it is offensive to our self-sufficiency to label Christianity as a crutch. In other words, the only people who will ever come to get what Jesus has to give are sick people, people who know that they are spiritually and morally and very often physically crippled. Everybody has a creed.
All people believe in something and shape their lives around it.
We all have a creed that we live by, whether we can articulate it or not. It captured the spirit of the age, and the spirit of our age. Trust thyself, every heart vibrates to that iron string. Discontent is the want of self-reliance. It is infirmity of will.