I have seen BPers defend this time and time and again, so i thought to bring this up here.

A husband has been married to his wife for 5-10 years. This is specifically where the marriage was taken to be monogamous, no poly-amorous arrangements here.

One day, the wife suggests the idea of a MMF threesome to the husband. The husband, has not expressed a desire for a threesome, with any combinations of genders before. Also, the male in question to be brought in is much, more attractive and physically fit than the husband, but the wife has absolutely no history with the new male.

So, is denying your wife of this opportunity selfish or cruel in any way? Or is the husband correct in speaking up for himself and not standing for something he doesn't feel is comfortable for him?

By denying, I mean that the husband will not participate in the sexual encounter, not that he will restrain the wife physically in some way.