I absolutely agree that it's very one-sided, and I am absolutely certain that you are right that there will be relationships where the DIL is in the wrong. However, to state the obvious, that one-sidedness is a function of the demographics of this site, and the voices that emerge from that demographic. All we have on the internet - a medium singularly denuded of nuance and tone - is the voice of the particular poster in front of us, and I'm not sure that it always helps to question, systematically, every one of those voices. It is a bit like saying over and over again on the relationships board "Oh, well there are relationships where the bloke is trying but the woman is actually in the wrong, so we should question each one of these women forensically to determine whether they are actually at fault in order to ensure that a more balanced view of maleness is presented". While there might be a kind of 'balance' to presenting that view, to the poster at the heart of the thread it can feel a bit like gaslighting.
The other thing is that the nature of this site tends to mean that it's the worst cases of in laws that are discussed, not the best. Whenever there is a thread about good in laws, you hear a different set of people who have good, positive relationships with their MILs speaking up. Perhaps the way to redress the balance is therefore to create a separate discussion where positive intergenerational attitudes are fostered, and the warmer side of the in law relationship aired? Because there are plenty of lovely stories of truly inspiring and mutually supportive relationships that we perhaps don't hear often enough.
I'm all for tolerance, but I do think that relationships are two-way. Mutual respect is needed for them to work. Not being offered respect and space - not being given recognition (not in the sense of 'reward' but in the sense of 'recognition of personhood') by someone can be a surprisingly devastating experience.
To speak personally for just a second - the worst things that have happened to me in my life - violent attack, sexual assault, rape - have involved a lack of recognition of my personhood, of the fact that I am an individual with feelings and desire that are worthy of being heard. I find that when my MIL interrupts me, talks over me, and treats me like a 5 year old, it makes me feel surprisingly similar to those incidents. It's not as strong or as devastating or as terrifying, but it is the same feeling, just a little more diluted. And I hate feeling that way. I honestly don't see why I should be expected to suck that up just in the name of keeping her happy. Why does her happiness matter more than mine? She is the one who has chosen this course of action, and she is surely able to treat people in a nicer way if she chose to. Sometimes, if you make bad choices about how you interact with others, there are consequences.