Of course they CAN be friends. Friends can share interests in activities and world views, and enjoy spending time together, without having sex (e.g. I don't have sex with any of my male friends).
When it gets tricky is when physical attraction attraction plays a role. To be clear, I do have a "type" (aka a "spec") of women that I'm physically attracted too. If you have compatible personalities AND are physically attracted to each other, the question becomes "why not do it". When that doesn't work out, my experience is that we generally no longer remain friends. I can only think of one women that I was friends with, started having had sex, stopped having sex, and then remained friends with her.
Now, IMO, if the attraction isn't mutual, it's not going to work out. Someone will always be scamming / manipulating the other tying for a hook up:
- bad mouthing your girlfriends
- trying to sabotage your relationship
- trying to get you drunk / impaired to take advantage
- "casually" introducing opportunities for a liaison
- etc.
So, I find it best to just avoid that whole scenario.
And of course there is the "significant other". If it's credible that at least one of you isn't physically attracted to each other, the significant other might not be an issue. I have a friend, for many years now, from an old employer; her and I do things together and her husband has no issue with it, but she is totally not my spec. BUT if the significant other thinks you are, or should be attracted to each other, they probably wont trust it. I currently can't see my one friends because her boy friend does not believe that I am not attracted to her (even though I have never even kissed her or wanted to). It's real tough with the boy friend of the one girl I did have sex with, and he's a buddy of mine (he don't trust at least one of us).
And of course if they have an incompatible personality, you probably aren't even trying to be friends. Some of my favorite girl friends had incompatible personalities with me
TLDR:
Yes, easy - Shared interests / beliefs, neither is physically attracted to the other
Yes, tough/risky - Shared interests / beliefs, one is attracted to the other but not mutual
Nope - Divergent interests, only physical attraction (mutual or otherwise)