Hi OP, your thread has hit a MASSIVE chord with me because you sound like my DH. I have 2 DCs, he is their step dad, and we have exactly the same arguments as you describe, even down to the 'toilet crimes' and underlying resentment we both feel sometimes.
I react much like your husband. I often feel DH only ever criticises the kids, and rarely notices when they do something good or kind. I am not a pushover parent by any means, but when I hear "X is so selfish/ungrateful/thoughtless", it brings out the defensive in me. It feels like constant moaning sometimes. I feel defensive because I interpret it as criticism of me as a mother. That I have somehow brought up feckless kids. Which I haven't.
On many occasions I have asked him to criticise the behaviour, not the identity of the DCs. If he called them "filthy pigs" like you did in an earlier post on this page, I wouldn't be able to see past that judgement on their identity. Whereas when he says "one of the DCs have left a dirty toilet", I also get cross with them and enforce cleaning it up.
My kids do a lot around the house - they cook, they do cleaning chores, and they always help clear away after dinner. They aren't teens who are going to grow up incapable. I am regularly complimented on what delightful teens they are, and how they are helpful and polite. It sometimes feels that DH wants them to be perfect, and never make a mistake. It is a big stress for us in our marriage tbh.
I have tried to explain lots of times that I need to hear the positive as well as the negative.
I don't know if that helps, but I thought maybe it would be useful to hear the perspective of a parent in the same situation.
If not, it helped me to get it out!!! 