From my 43 years experience in viewing how the world works...I, and I might add this is my perception from experience and also from speaking with people of the opposite sex intensively, have seen that many problems DO arise from male/female "friendships".
From experience and talking to many men on this subject I can see that it is much harder for a man to keep a friendship as just a friendship if there is ANY physical attraction at all. For a woman we deal with the emotions much more than a man does. We are able to seperate friendship from a sexual experience much better than a man can.
Not to say that either way of dealing with this is the better way...just stating that it can become a bit sticky situation (no pun intended) at times...simply because men and women are made very differently.
I feel that a special platonic relationship depends upon these 2 criteria:
1) That you can keep a friendship as just that...a friendship
2) Our spouse/significant other can accept this friendship.
My personal opinion is...if our significant other cannot accept (what we view as a platonic friendship) we have a few choices to make. A few things to consider are:
1) Figure out how much our significant other's views matter.
2) Are the views of our significant other valid?
3) Do we love our S.O. enough to understand how they feel or do we do what we feel is right for us?
Choices like this are not always easy. What "we" may feel is totally innocent in the beginning, may become something other than that as time passes.
What happens in situations like this is that we have to be levelheaded and decide what is the best situation for us personally. But always remember that things happening, even with the best intentions, can get out of control and hurt others.