Not so surprising for a person who never emotionally matured beyond a 14 yr old, whose parents and adults around him coddled and excused his behaviors as being an imp, a jokester, etc.
As for the people around him, in their 20's they probably found this funny and maybe still did (lots of people don't grow up until their 30's or later). He got attention for his behavior and got the yuks from his guy buds and lots of people wanted to be around the outgoing guy.
At some point normally developed people no longer find his brand of strange amusing. Some people in that circle had gotten to that point, some didn't.
This is a great point...Jason never grew up, simple as that. Being the class clown and life of the party is typical for children, perhaps even stretching through college/early 20s. But at a certain point, most people grow up, or at least know the boundaries of what is socially acceptable. A side story to the trial was how Jason Young's former friends seemed to distance themselves from him, and certainly didn't zealously defend him. Curiously, the highway patrol witness seemed like his closest friend.
Unfortunately, being a sociopath, Jason Young's "Peter Pan" complex was only compounded by his family's adoration and "oh, that Jason!" attitude. He was never disciplined or taught responsibility. His treatment of women outside his family belies a notion of entitlement, and that he was not to be questioned. Despite these character flaws, the guy clearly could charm women and enjoyed it...sadly, Michelle Young was fooled by his false charm.
Jason was not wired to coexist with a strong-willed woman who was his equal, in marriage, and would stand up to him when necessary. To Michelle Young, she likely never viewed herself as "standing up" to him at all. They argued like most couples, maybe more than most, but by all accounts it was never physical. The second pregnancy lit the fuse. Jason Young became a timebomb, and he delayed the fuse in his first attempt to kill Michelle. When that failed, he realized he would have to do whatever it took to avoid being further "locked" in marriage. To a woman to whom he could not relate and whose mother was worse (Jason's worldview, mind you). They argued over the family holiday plans, he could not imagine living with Michelle
and her mother.
By this point, the bomb could not be stopped. Jason was not going down this path. That's where his sociopathic mentality overruled any sense of logic that the vast majority of us possess. He did not proceed with consequences in mind, empathy (clearly), or obviously, logic. His reticence to this restrained lifestyle overtook common sense, and was compounded greatly by his hatred of Linda.
Psychobabble aside...I'm just relieved that Young is where he's supposed to be and pray that Michelle and Rylan can look down and offer some comfort to their loved ones.