First off, nobody was in a "frat". The correct term is fraternity. Sorry about the semantics, but the effect it has on me is sort of like when someone calls me "a gay".
The fraternity I joined left a long and positive effect on my life. My chapter was founded by some outstanding individuals, and has set up an organization in which young men are able to become better people than when they came in. One of the fun things is that you are beholden to each other as brothers no matter one's religious beliefs, political beliefs, personal interests and activities, sexual orientation, or socioeconomic persuasion, and you learn a lot through interaction with people from all different backgrounds. You learn to appreciate them, and they also learn from you and appreciate you as a person. In fact, I found them to be some of my brothers to be the most inspiring and upstanding individuals I've ever met.
We are humans, based on a need to be social and belong to a community. I feel that guys, in particular, have a difficult time finding the socialization they require with other guys, due to the fact that society sometimes ostracizes the display of male emotion and affection (the idea of bromance being a very modern creation) For many men, these peer groups are organically created among groups of friends. For some, the camaraderie they desire are also found in group activities, such as athletic/sports teams.
For many men, when they come to college, they unfortunately leave behind their previous high school social groups and friends. Some may find it among floor mates in their residence halls, others may be lucky enough to have preexisting connections among their classmates. It's not easy though, and though a lot of college men may create friendships, a lot who joined my fraternity expressed that they wanted to find a core group of guys that they could become friends with, aspire to learn from, and be a part of.
Most of the guys in my fraternity never came to college with the intention of joining a Greek organization. We studied hard, did volunteer work, debated over social and political issues with each other, participated in campus activities and community events, and were a positive presence with our university. We took care of our brothers when they needed it - a brother who had a parent pass away unexpectedly, a brother who was suffering from severe alcoholism, another suffering from cancer. It's kind of like a giant extended family that looks after you, and you look after your brothers, much like any other community. We also had a lot of fun, partying and doing all sorts of shennanigans.
I attribute my success as an individual and as a health professional to some of my experiences in the fraternity. It helped to make me a better person, a better man. I then get to pass down what I know and help others who come after me in the fraternity.
Aaanyway, here's the tl;dr - Fraternities can be a positive experience (if you pick the right one), fraternity = organized bromance