That’s the part that bugged me most when I was in youth group. My own congregation never really took a stance on the creation debate, but there were guest speakers at certain functions who were of the zealous type. You start to lose a lot of respect for speakers when they start pushing claims that you know not to be true. It’s kind of hard to unsee the facts.
Earlier in your post you also spoke of going through the evidence yourself, and that is also something that is hard to undo. Once you develop and train your ability to critically evaluate scientific findings it is really hard to untrain it. When you see all of the pieces of a theory falling together into such a neat and tidy package, a theory that passed all of these massive hurdles that could have disproven it, you really can’t pull back from that.