Why are the opinions and decisions of the Founding Fathers of America always considered so infallible?

I understand they were brilliant men who did amazing things during their lifetime. Please do not think I lack respect for what they did. However in my opinion people put what these men said and wrote on too high of a pedestal. They lived 200+ years ago and while I'm not suggesting they be forgotten, it does seem silly to ignore how times have changed since their lifetime.

For example the Constitution and Bill of Rights are brilliantly written but suggesting that it is flawless like many do seems narrow-minded. It seems people are frightened to question anything the Founding Fathers put into place.

TL;DR If you are ever in a discussion with someone, a common fall back is "the founding fathers created this nation on these ideals!" and no more argument is to be had.