Why? Because if you are not in a committed relationship, you are not obliged to be "loyal". Women understand this, as they do not date exclusively (generally speaking). So why should we? Because all that the phrase "spinning plates" means is dating non exclusively. What it doesn't mean is that you are allowed to cheat, after you said you won't.

Furthermore, there are quite a few studies showing that women are likely to have a "plan B" even in a committed relationship, and (at least in my opinion) there is nothing wrong with this, given that for you guys, it's very important to feel safe. So i would argue that keeping your options open, without excercizing them is acceptable for both sexes, especially in the first couple of months within an LTR. No one should be shamed or ridiculed for it.

Expecting your men, not to have female friends, while you have a "plan B, C, D..." is utter hypocrisy, and is has no justification whatsoever.