UTG has the worst position preflop because he is the first to act after the BB. Postflop, he obviously has position over the blinds. 

UTG is definitely not the worst position. You'll make a bit on money playing from UTG, but you can't make money out of the blinds, against solid players.

If UTG play weren't profitable, you could just fold 100% and still break even in a non-ante game.

Any other reason UTG is the worst position? Well for starts you are the first one to act PF which means you better have a damn good hand if you want to raise given that everyone else is ahead of you. Secondly, think about it like it's an auction for treasure in the middle of the table; the only catch is that you only get two times to bid unless you want to potentially bid all of your money and have the risk of ruin the third time. That being said, you don't know how much the others will bid so it will be very difficult for you to successfully make a profitable bid if you are the first one to act. Position really holds so much power in poker. If you you're at all skeptical just having a look at any winning players stats and you'll see that most of his / her VPIP will be comprised of plays revolving around the CO, BTN, and SB as they hold the power seats. Furthermore, think about holding AA or KK UTG.. If you don't raise big it's going to be a huge waste of equity and you'll run the risk of not thinning the field and having smaller suited broadway / lower connectors potentially crack your pockets, and if you do raise big your range is going to pretty obviously read as huge given that you're UTG, and if you limp with the intention of reraising there is always a big chance of having a family pot ensue which isn't helpful to your cause either.