Platonic friendships with opposite gender is possible, but difficult to maintain that balance. Both parties need to respect boundaries and do not cross that line. It is difficult especially when one starts to feel too emotionally connected and involved with the other and wants to go beyond a friendship. Therefore, platonic friendship IS possible, but both parties need to respect and understand that there are boundaries, ie, if both parties already have their own spouses. So both need to respect that they cannot be anything more than just friends. Clear communication needs to be set and there must be trust and respect (as friends), not to overstep boundaries. It just feels childish to know that some people cannot be friends with the opposite sex because they're easily swayed and they are emotionally vulnerable enough to do so. Are people not firm enough in their own marriage/relationship? People need more self-control. I believe if both parties in a platonic friendship are already in happy relationships/marriage with their own respective spouses, they have no reason to sway and their hearts will not be vulnerable enough to start falling for each other.
Only people in vulnerable and emotionally distant/emotionally empty relationships/marriages will find themselves starting to sway and fall for their platonic friend.
I believe there are definitely people who have enough self-control to know what are the boundaries, please. As long as people have a sense of responsibility, platonic friendships are possible.
However, do not keep secrets from your spouse and do not do anything that you would not want them to end up doing to you too. ie, to the men reading this, if you do not want to see your wife go out on a 1-to-1 dinner with her male colleague and keep it as a secret from you, then please do not go on a 1-to-1 dinner with your female colleague too and keep it as a secret from your wife.