While some preach their favorite ideas, you shouldn't think of that as being what Christianity is, but instead as being the viewpoints of those individuals.
Sometimes people can lose perspective and their ideas/theories can become more important to them than even God, though they don't realize this has happened. It's an "idol" when this happens.
When a person creates an idol like that, they mistakenly can think their idol is somehow the most important thing.
But only God Himself is the real worthy of making 1rst in our lives.
*If* we make God first, then we will not get trapped preaching a theory about creationism (or any other single doctrine that isn't the Gospel itself) -- when we put God first, then we want to learn and do as He said to us to do through the Words of Christ, our Teacher and Savior. Doing as Christ said will put any other doctrinal obsession into 2nd or 4th, or 24th place, and it will no longer seem the center of our mind.