It is allowed to take photos in most musea since what we see is public domain that is also why you find these photos on internet and wikiart, tripadvisor and Google Maps.

The average shop complains more than the average musea or church.

It was the old believe that craziness shows as soon as you lay down in bed. Who knows someone spreaded this believe once and like you know gossip goes fast and even lies are taken for the truth.
By the way, hundreds of years the wisdom didn't come from education, many didn't visit school this was mainly meant for the wealthy and religious ones.