If I had been asked this question when I was 8 years old, I would have readily told you, "Because they're SOOOOOOOO hot! I'm going to marry one of them someday! Just watch!" That pre-pubescent dream is long over. Now, at 20 years old, I have some different reasons; 4 to be exact.
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Reason #1:AJ
There are many reasons AJ tops my list. The number one reason being, his struggle with alcoholism and drug abuse. No, I'm not condoning what he did. I'm proud of him for having the courage to get out of it.
So many people, not just celebrities, have the same problems AJ faced, but one thing a lot of people lack, that AJ had, is the courage to stand up and say, " You know what? I have a problem, but I'm not just going to sit around a rot in it. I'm going to get help, and I'm going to fix it."
Many people may look at AJ, see all his tattoos, read about his past, and immediately forbid their daughters and/or sons, to idolize this 'junkie'. If they would just take the time to see what we all, as fans, see, they'd realize that underneath the 'bad boy' persona from the early days of the group, is a man looking for acceptance and just wanting to be loved.
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Reason #2: Nick

What can I say about Nick? He's been through a lot as the group has progressed over the years. From joining the group at just 12 years old, to his mother writing a tell all book about him, to his infamous DUI, dating Paris Hilton, to he and his siblings doing the reality TV show, 'House of Carters', where they aired all or a lot of their dirty laundry. Throughout all of this, Nick has come out on the other side, a good, caring man. For that I'm proud.
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Reason #3: Brian

Brian is a son, husband, and loving father, to a beautiful little boy, Baylee. He didn't always have it so good. Brian was born with a heart murmur. At the age of 5, he got a life-threatening staph infection, putting him in the hospital, where the doctors told his parents to prepare for a funeral because they didn't think Brian was going to live. Lucky for us, he did, and became part of the Backstreet Boys in April 1993.
In 1998, Brian went through a routine medical exam, where the doctor discovered that his heart was enlarging at a dangerous rate, and advised Brian to undergo heart surgery. With this coming at the height of success for the Boys, Brian put off the surgery. While touring, during breaks between sets in the shows, Brian would have to go backstage, where they had oxygen tanks waiting to help him with his breathing.
A few months into 1998, May 8th to be exact, Brian finally decided to undergo the heart surgery reccommended by his doctor. During the surgery, doctors found a second hole, which they repaired, and Brian has been living a healthy life ever since.
He's also done a successful solo album. A Christian album at that. In the midst of the pop world, where sharing your faith is frowned upon by most, Brian is open about who and what he believes in. Look at all the success he has to show for it!
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Reason #4: Howie

Howie had his fair share of trials in 1998. During the Boys' tour in '98, Howie was advised to get on the earliest flight he could, because his eldest sister, Caroline, who had battled with Lupus for 13 years, had taken a turn for the worse, and it didn't look good. Sadly, on September 12,1998, Caroline Cochran-Dorough, lost her battle with the life-threatening disease.
Now, at age 34, it looks like Howie will be the next Boy down the aisle. He and long-time girlfriend Leigh Boniello, officially announced their engagement and plan to marry in late 2007.
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Okay, so I lied! There's a fifth reason I'm a fan. Ready?
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Reason #5: Kevin!

Well, he may not 'officially' be part of the group anymore, but to us, the fans, he always will be. I admire Kevin for his sheer determination to start a family with his wife, Kristin, away from all the hoopla that is the celebrity life. While I may not have agreed with his decision at first, I am so happy for he and his wife, that the dream of parenthood finally came true for the on July 3,2007, when Kristin gave birth to their son, Mason. I'm proud of him and I know his father, Gerald, whom he lost to colon cancer in 1991, is looking down on him from heaven, filled with pride and joy at the success his son has become.
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So, again you ask the question: "Why Are You a Fan?" The reasons above speak for me.