There is known psychology behind this. If both are honestly turned on by it, both want it, and both are fully equal in the decision, fine. But a woman should never be forced, pressured, or emotionally cornered into sexual interaction with another man if she does not genuinely want it herself.
The more pressure a man puts behind something like that, the more likely he is to destroy her respect for him. Because then it stops being about mutual desire and becomes about his need being placed above her boundaries. Once a woman feels that her feelings matter less than his fantasy, something deep in the relationship is already breaking.
Even if she goes along with it, that does not prove real consent in spirit. People can agree outwardly while feeling hurt, conflicted, or pushed inside. And that is exactly where resentment, distance, and loss of respect begin.
You also risk creating a situation where she starts seeking it for herself, without you being part of it. And as we have seen here, some women end up losing interest in that part of the marriage with their husbands entirely.