JR was always sorta soft on the women in his family
He doesn't underestimate his mother, that's for sure.
so not sure it was uncharacteristic that he let Pam off the hook.
When did he let Pam off the hook? J.R. was regularly trying to ruin Bobby and Pam's marriage, exploiting any slight weaknesses. Pam was usually very wise to J.R.'s methods and can be feisty when directly challenged, which is why J.R. described her as "a thorn in my side since the day that she first arrived on Southfork".
A mean as he could be to Sue Ellen, he only put her in the sanitarium because the family practically forced him too.
His family forced him to do something about Sue Ellen's predictament, but I remember that scene where J.R. sweet talked both his parents into thinking that it was the right thing to do to put Sue Ellen in the sanitarium, where she'd get help, professional care etc. to get better.
He didn't run her through the mud during the custody hearing, because Miss Ellie asked him not to.
Miss Ellie is not to be underestimated. Season 5 DVD she was like a force of nature at times with the way that she acted in Jock's absence, and into Season 6 DVD when she almost broke Jock's will. She was on the brink of a nervous breakdown just before the Southfork fire though, another victim of the Battle for Ewing Oil, the in story explanation for her missing the first 11 episodes of Season 7 DVD.
Auch as he groused about Donna being at Ewing Oil after Bobby was shot, he didn't do anything about it. He didn't move against Pam or Lucy when they took John Ross to Sue Ellen.
Pam ended up in a sanitarium herself soon after taking John Ross to Sue Ellen. This happened despite most of the other characters thinking that Pam would have been the last person that would have suffered a nervous breakdown. J.R. helped a bit in that, with his cruel comments. But Pam taking John Ross off Southfork also hurt her at the time in a way that she hadn't thought of, because there wasn't a baby around Southfork anymore, so in that sense Pam thought J.R. was right when he was lambasting her for taking John Ross to Sue Ellen, lowering Pam's self-esteem further.
He was a dangerous man, but he pretty much left the Ewing women alone.
What would you expect him to do to them?