Why are First Class passengers boarded first on an airplane? Why would you WANT to board first? Thoughts of a career Coach Flyer. Help me understand, please..

I read this short article on the eternal problem airlines have in getting airplanes boarded in a timely and efficient manner.  One comment toward the end  made sense to me and  made me wonder. I will put into my own words.

Why do First Class flyers get seated first and why would they want to? (Disclosure:  I have NEVER (not even once) flown in First Class).

You are guaranteed adequate overhead space.  You have to endure the awkward stares and the wayward bags of the great unwashed (me) as we slowly shuffle past you.   I am sure people and kids say the darnedest things to you as well and class envy rears its ugly head.

Why would you not want to board AFTER everyone else? Seems like it would send a power statement (isn't that why you fly First Class in the first place?) to those of us in coach---this ain't leaving until we are on board.