I guess it depends on the situation. I doubt they could stay just friends if one of them is attracted to the other. In either way, I don't like taking too big of risks, so I just have one girl friend, and she is the girl I have a crush on. I make a conscious choice not to make friend with other girls.
Just in case I do happen to get in a relationship with the girl I have a crush on. And even if she doesn't care about me having female friends, I rather not get involved in a situation where she might get jealous in any way. Now, she has male friends, and I don't care. I just have two best friends, she is one of them. I don't really need more.
Here is my thought-out opinion, and I hope it matters to you.
Yes, guys and girls CAN be friends. But that is not the true question. The real question should be, can guys and girls be friends without having any attraction or sexual feelings get in the way? The answer to that is B - No. Men are designed sexually. Truth is all of a girl's guy friends have imagined a girl naked or imaged her having sex with him. I think girls can have just guy friends, but a guy can never PURELY have girl friends. Feelings do indeed get involved. Emotions rise through friendship, and compatability is shown in friendship. Therefore, attraction is easily created through the liking of one's personality and compatability and comfortability. There are many opposite-sex friendships that have existed through life, but guys can't ever see a girl as just purely a friend. Unless he thinks she's completely ugly (and even then, they only discover their nonattraction by imagining her naked) or they have already hooked up before. Most of the time that decreases sex drive and imagination if they've already had a taste of the cake. What makes sexual tension rise in friendships is the mystery of what it would be like to be intimate with them sexually.
This is just how I feel and what I have really observed and discovered throughout the years.
Woman have n more of a tendency to believe they can be friends and tend to be able to keep that distinction between the two better. Men on the other hand don't differentiate between the two as easily. If you want to keep someone a friend then you need to clearly set boundaries early and always how you talk about your current relationships with them. Once you go to far and allow to much intimate info out feelings tend to get in the mix between the two and then problems will occur.
It is a matter of maturity. I am friends with a girl who is very sexually active and I have had sex with her a few times. I am not interested in making her my girlfriend or ever marrying her, because she is a serial cheater. She is still a very good friend.
Yes it takes a strong bond. More times than not casual friends aren't really just friends on both parts. But I have two guy friends from college who are just that. We've been through shot together and I'm also good friends with their wives now. We have a common respect for one another as through the test of time we've each pulled each other out of the fire a time or two. That's what it comes down to knowing you have each other's back. If I find out through another source that one of them doesn't like my boyfriend I think very long and hard about it. These days with most the guys I date all my friends really look for is to make sure he is sincere and supports me. By support I mean emotionally not financially.
People may have good intentions, but more times than not, one will have an attraction to the other. It may not be reciprocated always. Onceones have been crossed, not even sexual, it's hard to just remain friends.
Maybe I just have cute guy friends. Call me crazy, but here's the math:
Cute guy + awesome personality + fun to be around + all that other good stuff = I want more than just a friendship.
My best friend is a guy. We are like brother and sister. He's a very attractive young man, but I'm not attracted to him. I'm a very attractive young woman, but he's not attracted to me. Simple as that. Brotherly/Sisterly love for the WIN! <3