If you are an author (or a human, really) you are going to have to find a way to deal with rejection. Please don't go attacking agents, or editors. This sort of thing rarely helps your cause. I know it's not fun, so cry, beat pillows, eat ice cream, whatever helps you through. You've got to find something that doesn't involve assaulting people.
My first real taste of rejection was the college admissions process. Until then I'd been one of the smarter kids in my grade and felt I could do stuff pretty easily. I also had big plans about The Future--all of which involved me becoming Very Important. And then colleges I applied to said to me, "Actually, you're pretty average. Sorry."
I had this fantasy that one day they would be sorry. And since I was going to be Very Important, they would invite me to speak on their campus. I would respond by sending them a copy of the rejection letter they sent me. ("Due to the the strong pool of applicants, I regret to inform you that I will not be able to speak at your Very Important Thing...")
And I used that whole "prove them wrong" thing as motivation to do well at university and later at grad school. But I don't have copies of those rejection letters anymore. I guess that's why the "use it as fuel" metaphor is often used. Fuel is good to get you places, but eventually it burns away.