If there is no hell, a good many preachers are obtaining money under false pretenses.
The word of God is complete, and those who don't preach the word in its fullness are false teachers.
The Galatians are severely censured for giving heed to false doctrines, and are called to pronounce even an apostle anathema, if he preached another gospel.
To thine own self be true, and it must follow, as the night the day, thou canst not then be false to any man.
Preaching is to much avail, but practice is far more effective. A godly life is the strongest argument you can offer the skeptic.