No, you're not the only meanie.

I've been in a step situation for 7 years (married for 5) and my steps disregard my very existance. For a very looooonnnnnngggggg time my DH apparently refused to "see" the behaviors let alone address them.

It's difficult not to have resentment when you are treated poorly by 1) children, and 2) in your own home. My feelings are this: Things should have never been allowed to spiral out of control, and now it's pretty much too late to stop that bus. That's on DH, because he would never say anything, nor would he ever support me when I tried to say something. And yes, as much as I hate to say it, there were times when HE wasn't exactly setting a stellar example of how to treat/respect me in front of his kids, and they are what they learn. Secondly, the SS's were and are old enough to know exactly what they are doing, and their behaviors are wrong. But they don't care. So I told my DH that I don't care either.

But much of that comes with a price. I've disengaged from them. I do absolutely nothing, emotionally or financially. See, that's the clencher -- my DH never had a relationship before me (meaning, with the non-working BM) where both adults worked, had healthy incomes, and could enjoy the finer things in life. Now he wants to be able to "share the wealth" with his kids because "they deserve to reap the benefits too". Not gonna happen on my dime. We ended up separating finances because I resented the fact that they were allowed to behave in a negative manner towards me, yet DH would "reward" them with goodies purchased with OUR money (note: DH makes good money, but most of that disappears every Friday in the way of CS... to which the SK's complain their BM uses for her, not really them. So whenever they want something they come crying to DH. Fine, DH. You can spend $ on them all you want after you pay your portion of the bills -- and have $87 left over before you've filled up your gas tank).

Flip side, I'm very careful with my money, don't have lavish stuff, but am financially able to give my kids extras and do so when the need arises or I feel like it. So yes, that makes me look like even MORE of mean stepghoul because I buy things/do things for my kids and NOT the SK's.

But the bottom line is this: they've made it clear I am NOTHING to them. If they can't accept my presence in their lives and the life of their father then they certainly should not expect anything from me, whether emotionally or financially.

I too disengaged - 8 years ago. If you want to preserve your sanity and stay in your marriage, the first thing you are going to have to do, is not to care how your SKIDs feel about you. I'm pretty damn sure mine hate me - that's ok - I don't care for them, either, but I tolerate and am civil to them for the sake of my husband.
It sounds like you have your SS full time - that's hard - I only have to cope with EOW. Try to be fair but firm with your SKIDs, you are not obligated to love them, as long as you treat them decently. You might want to read this article that someone else on here posted the other day, on the dynamics of stepfamilies : http://www.stepfamily.org/dynamics.html