I have this trait...but I refuse to give up my ideals
This can be termed having the courage of your convictions. In my view this is a great quality to have. Magaret Thatcher was "accused" of this and rose to become my country's first woman prime minister and one of the greatest ever. It was said she was the only one in the cabinet with balls. .

I am very dutiful (I wish I could get rid of that particular trait) and loyal,
Sounds like qualities every person and submissive should have to me.

But when it comes to myself, I tend to be more "illogical".
This comes from the caring for others quality. You can do crazy things yourself and can handle it if it goes pear shaped, but would not want others to make the mistakes. Most parents "suffer" from this when guiding their children to adulthood. "Don't do as I do, do as I say" is the maxim.

I would rather go hungry than not speak up against wrongs being committed.
As I have said in other posts "All that is required for evil to prevail is for good men to do nothing". Why is it irrational to to have a "need for freedom and right". Is that not what the founding fathers of your country fought for.

I think it is highly unlikely I will ever get married
You just need to find a likeminded partner.

for the wrong reasons and they often don't mean it..after all there is always divorce.
One could say the same about Ds partners and collars. People get together for the wrong reasons.

Yes, divorce is a necessary evil
Not if time appropriate time was spent ensuring the partners are matched. If and when storms come it is the strength of the relationship that will help them both negotiate the rocks and weather the storm.

Perhaps this has to do with me placing the value on marriage as a spiritual commitment, and not as a social institution/convention
This dilemma can be easily avoided in the vows the partners make. If you say til death do us part before God then it is spiritual. The problem is many want a church wedding for the tradition or romance of the ceremony without giving thought to the contract they are making with God as witness.

I don't understand how you can stand in front of God, or people, give your word, make a commitment...then one day take it back, just because its no longer convenient, because you have found something better
I suggest you read about Sir Thomas More or see the oscar winning movie/play A Man For All Seasons. This explores the concept that divorce is breaking a solemn promise to God.

Which brings us to the matter of infidelity...
The problem here is not being honest in the partnership agreement. If I tell my partner upfront, hey I got a wandering willy and she nonetheless takes me warts and all then there is no problem. It's the deception that is the problem more than the infidelity. Most woman in my view don't worry too much about a guy being unfaithful (ignoring STD's of course) it is the possibility of a rival and being dumped. If a guy goes to a whorehouse no big deal but if he has a mistress then it is.

I began to question - is it really too much to ask of men to be sexually, as well as emotionally, faithful?
Let's go back to our animal instincts. The male has the desire to plough the field and scatter his seed to procreate and preserve the species. The female is concerned with rearing the young and needs the male to provide the food and protect against danger. I am not an anthropologist but that's the bullshit excuse I give when I get caught out, it's wasn't me it was the animal inside me. - haha just joking,

How do you deal with infidelity,...especially when there is an added element of bdsm involved?
For me in both ol and rl relationships it's not a problem because I discuss and sort it out upfront with my partner. I take the view WYSIWYG - what you see is what you get - and then it's up to the gal to accept me for what I am or reject me.

Men marry women with the hope they will never change. Women marry men with the hope they will change. Invariably they are both disappointed. -- Albert Einstein