Whether married, dating or single, do you think it’s perfectly ok to have friends who are the opposite sex/the sex that you’re attracted to?

I’ve heard it from both sides - one side says it’s no big issue, and that’s it’s perfectly normal to be friends with the sex that is if the same sex you prefer. As long as there is mutual respect with one another.

However I’ve heard the other side say that there’s no such thing as being just friends with the sex you have a preference towards. That as adults we are more prone to having inappropriate boundaries crossed by being friends with guys if we prefer guys, or girls if we prefer girls. This side claims that you are better off establishing firm boundaries and not having friends with the sex that you prefer.

What are your thoughts?