Yep, they sure can! Anybody who tells you otherwise is suffering from one of the following three social delusions;
1) that everybody of the opposite sex is so physically attractive that it renders plutonic relationships truly impossible,
2) that everybody of the opposite sex wants them bad (a.k.a. a delusion of grandeur), and
3) that the only thing that can successfully cross the gender divide is sexual in nature.
First and foremost, people are drawn to each other for a variety of reasons and they aren’t always physical. Some people will come to be very close friends, some will be acquaintances, some may even evolve in to enemies, and yes, some will even become love affairs, but no one thing will ever define which category any given person will fall in to for you. It isn’t defined by race, religion, social standing, looks, intelligence, athletic abilities, the clothes they wear, the things they own or the way they talk, and it isn’t defined by gender.
People grow close for complex reasons and that closeness is made stronger by things like having similar values, common goals and shared experiences in life. You can have these things with anybody regardless of gender and the fact that they are a person of the opposite sex does not mean that a relationship has to be romantic or even physical in nature. A well-rounded secure person is able to have different relationships with different people and get different things out of the relationship without ever deconstructing that relationship down to a gender based stereotype.
In other words not everything in life is about sexual attraction and to suggest that a friendship between a guy and a girl will always be plagued by sexual tensions is naïve, sexist and just plain ridiculous! Yes, yes, yes, guys and girls can be friends. In fact I would be weary of people who don’t have any meaningful plutonic friendships with people of the opposite sex. Anybody who is comfortable in their own skin won’t choose friends based on something as superficial and unchangeable as gender.