I can't say I'm particularly opposed to opposite sex friends, but it's probably safe to say that I'm indifferent about having them. I gravitate toward girls for sure - I know that I long for their approval and also crave their guidance and support. I suppose I'm not that good at "being a girl", so I've got that longing for "sisters" who can watch out for me and teach me. It's still pretty hard for me to assimilate, but even when i make guy friends, i still prefer the girls.
When i was a kid, i had a lot of male friends as well as some female, but i had very boyish interests, so my female friends were tomboyish like me. However, even my tomboy friends could also be "girly" and had the girly friends as well. I could never understand it. I remember going to a friends sleepover and being appalled by the cattiness of her other friends (not to mention, very confused by it). As i got older, being friends with boys became "weird" and awkward for reasons I couldn't understand, so I guess that's when I started trying to learn the girly ways of the girls so that I could mesh better. I guess I never got around to figuring out the social rules of interacting with the opposite sex as a teen (and adult), so I just sort of steered clear. Oh well.