In terms of gender roles, you may see men as a "threat" and women as "harmless" because society has taught you that men are aggressive and strong - the aggressor and seducer, and competition for "the women" is part of that.
In terms of sexual orientation - part of the traditional view on how people should conduct their love life is monogamy, and another part of it is heterosexuality. The part of you that has abandoned this traditional view by embracing polyamory is also embracing all deviations (
) from heteronormativity (and therefore - sleeping with other people = great! sleeping with women = great!).
But, there is a little bit of old thinking "left". Rejecting anything that is not the norm
. Which is when the "ugh" feeling kicks in (sleeping with men = bad). But, when your wife sleeps with a women, that situation is already so far removed from traditional-old-"ideal" norm because of the same-gender-interaction that the "ugh" doesn't kick in. See what I mean?
In a similar vein, some people feel that homosexual sex is playful and sexy and fun, but heterosexual sex is 'meaningful' and part of 'a greater romance'.
Now, I am not
saying you actually think
any of these things at all. I am saying we are all conditioned by our cultural upbringing and that may influence our emotions some times.