I think everyone is suffering in an economy that hasn't yet recovered from the disasters of the last 10 years, and it's doubly hard to be excited when you are in an unstable marriage and exhausted from small kids. The holidays are very stressful for most people anyway - trying to make lists and get stuff bought and wrapped and mailed, get the cards sent out, the house decorated, and so on. I don't think you should feel compelled to participate in everything and apparently you grew up thinking that the men should decorate and not the women, so you carry that into your current family where it may conflict with your husband's traditions. Hence you fight.
The gift thing is out of control, in my opinion - it stresses out parents and gives kids a huge sense of the "gimmes" - gimme this, gimme that. Try to avoid malls and the canned Christmas music. Buy a few things for each kid, and make it things they will enjoy playing with rather than a contest to see how many things are under the tree. Don't give to as many people - if you feel you need to do something, try making cookies or something else that says "I care about you" without costing a fortune. If you have family in the same situation, discuss honestly the issues at hand, and maybe agree not to buy gifts for each other. Or, organize a Yankee swap with a $15 limit - it can be so much fun and will get you laughing!
I don't think you have a huge distaste for Christmas as much as a distaste for the commercialism and fake sentiment. You could also try donating some of the kids outgrown clothes and toys - go to a local place that collects gently used items for needy children. It will get you in the true spirit of the holidays.
If it would help, you could find a local church and attend a service - I know you said you are not that religious so I'm not pushing that, but at least what goes on there is about the true spirit and not the gifting frenzy. Also, the clergy do free counseling and deal with this issue for a lot of their parishioners.
I don't think you can force yourself to be happy. Not sure if you have thought about counseling - either for yourself or for you as a couple, but that can help and give some clarity.
Good luck.