Broom Kid said:
“Luke wouldn’t do that” is a very strong statement, and definitely a valid one.

That is the main issue I think. For some, the events described don’t tally with their vision of Luke. For others of us, it does. I think the main focus is on whether you actually saw who Luke really was during the OT or not. If you take him as fallible and human as I feel he was portrayed, his actions between ROTJ and TLJ are in keeping with his character traits. If you take him as founder of the new Jedi order and don’t let him be human, you won’t like what this story has to say. The important lesson of this saga is that we are all human and fallible. Some fall further than others. Luke has a history of making mistakes and being hard on himself. He has great passion but he can be easily discouraged. All we have in the tale of the fall of Ben Solo is a case of Luke being discouraged by those events. If you don’t think he would act that way or be discouraged then I think you have missed something about the entire saga. Try watching TESB and TLJ back to back. Then tell me that TLJ isn’t in character. Yes, in ROTJ, he is more confident, but confidence can be shattered easily. Luke has shown that to be the case. Insisting that he maintain the confidence that he has for most of ROTJ is unrealistic. The unsure Luke we see in ANH and TESB is just hiding under the surface in ROTJ and only needed a sufficiently horrible event to bring it out.