1. They're the best data we have
2. We have no reason to believe they're incorrect
3. There is REALLY no reason to believe they're dishonest
Is 100% intellectually dishonest.
This is exactly what happened 4 years ago, and apparently some people have not learned from their tremendous mistake.
If you want to know why "turnout at a campaign event" is a crappier metric than "real actual scientific data", I don't know how else to help, other than to point to other instances in which it has failed:
"Mitt drawing larger crowds" http://www.politico.com/story/2012/10/mitt-drawing-larger-cr...
"Donald Trump continues to draw YUGE crowds. That matters less than he thinks." https://www.washingtonpost.com/news/the-fix/wp/2016/09/28/do...
"Trump brags about crowd size but will it turn into votes?" http://bigstory.ap.org/article/d74fbd472f7a420a90737e55cfb20...
I do not know or care who you support in the Presidential election. However, I suggest you get realistic about your metrics, as you're way off in fantasyland at the moment, as far as I can tell.
If you turn out to be incorrect, I hope you learn from this experience. I know I will, if the data turns out to be wrong.