Monogamy and commitment are different things entirely.
On their own separate merits, I don't disagree, but if you are speaking within the context of a romantic relationship, they are pretty much the same thing. You are either committed to that person or you are not. That doesn't mean there has to be commitment for the relationship to exist. You can have an open relationship based on love and respect, as long as both parties agree. But that isn't commitment.
Whether you like it or not, we (as a society) have developed certain social mores. One of those is the expectation of fidelity within a serious romantic relationship. Sorry, it may be contrary to biology, but that's the way it is. But nobody is bound by this. Millions of people get around this by not committing themselves to one other person. If you can't be monogamous, fine. But you owe it to your partner to be honest. Maybe that spells the end of the relationship, but IMO, it's better than having to be deceitful for the duration.