I have to admit, sometimes the reactions seem extreme. My mom was a person of strong opinions, especially around child rearing. They were based on what she learned as the latest science and best practices recommended by doctors when she was in nursing school back in the early 50's. She gave very strong feedback to me when DS was young, especially around his sleeping in our bed (she was adamantly against it). Maybe there was more, but I am very much an 'eh' person, and it never registered with me one way or the other - I either took her advice or didn't, and that was that.
10 years later, she's doing a lot of childcare for my DB and his wife. My SIL was a lot more sensitive about things than I was, for many good reasons - this was her MIL, not her mother; her history with her own mother, which was all about criticism; a totally different stress level in her daily life, etc. And yes, my mom did things that were not right, like feeding my nephew McDonald's every afternoon because she thought he was too skinny. She did that because that's what my DB's pediatrician told her to do for him back in 1970. In her mind, there was a problem with one of the kids and no one was addressing it. She loved all of her grandkids and would have gladly done anything for any of them, but I can see that she definitely overstepped her boundaries.
It makes me sad to see so many people jump to 'I would never let her see my kids again!'. Certainly there are time when that's appropriate; no child should be subject to physical or emotional danger. But sometimes it's a more benign situation, where Grandma is annoying, maybe letting the kids get away with something they wouldn't be allowed with their parents, but not ultimately harmful. I think of how heartbroken my mother would have been, not only to have her grandkids taken away from her but at how actions she thought were for the good of the kids were perceived as evil and manipulative.