Is it really too much to ask of men to be sexually, as well as emotionally, faithful?

Probably. That's why I only get sexually and emotionally involved with women, although they too can have problems with being faithful.

Why would you marry someone with whom you are not honest, someone to whom you cant trust?

I assume that those who do so, have good reasons for their choices--it could be they need safety or security for their children, for one.

How do you deal with infidelity (in more conventional relationships),...especially when there is an added element of bdsm involved?

I make it very clear in any relationship that I'm in, that I don't share with anyone else. If they don't agree with that basic tenet, we go no futher. If during the course of the relationship, they are unfaithful, they will never touch me again. PERIOD

What do you consider infidelity in bdsm? Is there such a thing?

BDSM doesn't necessarily mean free-for-all orgies. I totally believe in committed partnerships and feel there is no need to bring anyone else into our play. Infidelity in BDSM is just like that of any other relationship--having a physical/emotional connection outside of the primary relationship. I think all parties need to communicate openly what their needs and desires are. With clarity and honesty, you can have faithful BDSM relationships that satisfy everyone.

Or does the dominant get to do what they want? What about sub?

Again, this would be up to the individual players. As the Dominant, I don't play with anyone else and I don't share my girl with anyone. I expect her to do the same.

What about domming and subbing others, is that considered infidelity?

If you both have communicated that part of your relationship is to involve others, then no. In my case, Domming or subbing others, because of the intense emotional connection, would be infidelity.

What is considered infidelity in polyamorous relationships?

Just because your partnership involves more people, does not mean that relations outside of the group are acceptable. Infidelity is the same thing--going outside of the primary group for physical or emotional connections. Again, communication is key. As a group you must decide what the boundaries are and the consequences for when someone strays.

As far as your other issue:

Marriage has, since its inception as an institution, had more to do with social control and transfer of goods than a sacred bond. It was designed as a way for men to be sure that the children produced by the union were theirs and for Father's to safely transfer their wealth to the next generation. God only got involved because the church wanted to protect those same ideals.

Does that mean that a genuine committment made by individuals is worthless? Not at all. Committments like marriage serve a number of needs, from a way to achieve social acceptance, to the financial benefits of the tax code, to mutual satisfaction. I believe that entering one is a serious decision and should never be taken lightly. When you give your word to love and cherish, you should keep it. However, circumstances can change(some people grow and evolve, some people devolve) and you should be free to reasses if what you agreed to do is still even possible. If your needs aren't being met, then you should end the relationship.