To "you don't HAVE to use it if you don't like it":
Yes, you do. If someone finds an ultra rare item and they don't need it and it sells for $80, do you think they'll put it on the gold AH? Definitely not. This means that the gold AH WILL have more items, but won't have high end items. The RM AH will have all the high end items, and if for some reason that $80 find does go on the gold AH, it will be bought and re-sold in the RM AH so fast us normal players won't even have a chance.
This part reminds me when voice chat started to come out and people were very hesitant about it because of the harsh reality of peoples disrespect towards each other. they also said don't use it if you don't want to however; without the voice chat it was impossible to cordinate units. (was a fighter jet simulator game from back in the day)