How in the name of sanity is it safe to have a sat nav stuck on your windscreen?

Please don’t answer with what others have said in early posts, that you can just listen to the voice directions, because if that is the case why have a screen in the first place. If there is a pretty looking moving map on a screen, human instinct alone will make you look at it especially in built up areas where you are not sure of the voice command instructions. it never ceases to amaze me what the law allows as legal when money can be made. Just look at those ghetto blasters how you can possibly concentrate on what’s going on around you as for hearing other cars horns or emergency vehicle no chance