I know what you are talking about. I am still having similar conversations with my fiancee. Several things we've discussed, hopefully they help you in your communications with your wife:
I told my girl that at all times and all places I'd always be protective & caring of her and that all of that is true regardless if i am not jealous of the idea of her having her way with another man.
In many peoples' minds "monogamy" and "loyalty" are one in the same. This idea is preposterous and based on what we have all been told about marriage our whole lives, but it does NOT have to be true about all marriages. Marriage is a study in trust. Boundaries define permission. What two people agree to and then abide by is what defines the marriage NOT a priori assumptions about what marriage "should be".
I've pointed out to my fiancee that a lot of the cognative dissonance she's had on this is because she has a preconceived "ideal" of what marriage is. When we dug into THAT and explored them we'd discuss whether she felt those "ideals" where actually requisite for a happy, fulfilling, committed marriage or whether such could exist in the absence of some of those "ideals". I think your wife has some "ideals" about how she thinks a husband "should act". Explore what's behind that together.
I asked her if she wanted a "jealous, fearful & insecure husband" or if there was something more to it than that, something underneath. She brought up the 'protective' issue & I asked her, yes or no, if it is possible for swinging husbands to be protective of their wives and still consent to their playing with other men? (Ofcourse) Ok, then jealous and defensiveness are not requisite to protection and loyalty.
I asked if it is possible for my protective-ness to be expressed in a way other than being jealous/defensive? (Ofcourse) So then we explored how i can demonstrate that in a way which reassures her that i protect her (or that you "treasure" her) and that there are ways OTHER THAN strict monogamy to do that.