I say that if it relates to the nature of the relationship, like sleeping with other people, then it is not fine without input from the other person. Either they can come to an agreement, or they can end the relationship.
well I didn't really get into the dynamics of it so much. The key words here are input and agreement, which is what makes it a relationship. It is a compromise between two different sets of wants. usually these wants will be the same in most cases.
But it is naive to assume that they will or can always be the same. That's my point. To expect them to be when they are not will lead to a break up in the relationship, whether by direct decision or by deterioration in intimacy.
You expect that your partner should respect your wishes to not seek to do something that you are opposed to, and that is fair, but it goes both ways, and you should respect her wants as something that is valid and worthy of consideration.
It may even be more valuable to you for her to be happy and to do something that she feels to be worthwhile, even if it is something that you disapprove of. that level of acceptance requires selflessness on your part, and it is rewarding to you when it is equally given back. that's why I say that people should be free to do what they want to. I think that will ultimately create more intimacy and a stronger relationship.
I think that knowing you are being held back from doing what you want will only lead to resentment of your partner.
Of course that doesn't mean that anything goes. You have to decide what level is acceptable, and where you can be flexible. Some things you may never be able to accept, and that's fine, it just means that you will not be able to have a relationship with someone where that is a factor. That happens. Not everyone is compatible with each other.