The act of shooting the President is not a rational one. There can't be a rational motive for doing so.
So the CIA's attempts to assassinate Fidel Castro were irrational?
I don't condone politically motivated violence or terrorism but political assassinations and terrorism CAN be rationalized if the killer intends to achieve some sort of political End.
I'm not convinced that Oswald had a political motive (assuming for the sake of argument that he acted alone).
If he was motivated by politics, it would still be wrong but not necessarily irrational.
There was something wrong with Oswald as demonstrated in many ways. His defection to the USSR. Not normal. His attempt to kill Walker. Not normal. His desire to defect to Cuba and trips to the Cuban Embassy. Not normal. Whether he had some type of clinical mental illness can be debated but there is no doubt that he was a very strange guy.
We agree that he was "Odd" and not normal for the times in which he lived.
But political idealism and strange behavior doesn't equate to mental illness.
If he had lived a few years longer, he arguably would've fit in with the New Left movements of the late-1960s/early-1970s.
Of course there are lots of odd people (some of whom frequent this forum) who never commit any violent act. But Oswald certainly falls within the category of suspect individuals. The FBI was keeping tabs on him. His own wife went to check on whether his rifle was still in the garage when she heard of JFK's assassination. That speaks volumes that his wife was suspicious that he might commit the crime even before the police arrived. He was the type. That doesn't make him guilty. That is what the evidence proves, but Oswald's personality is entirely consistent with being the assassin and nothing about his alleged lack of "motive" casts any doubt on his guilt as was suggested. That is not a defense of last resort but reality. Only Oswald can ever explain why he did it but it was no real surprise to anyone who knew him. He was a lifelong malcontent with a screw loose.
The FBI and CIA kept tabs on him prior to the assassination but there's no evidence that they viewed Oswald as a violent extremist.
J Edgar Hoover and the FBI spied on thousands of Americans from Far-Left activists to members of the KKK. Most of the people the FBI spied on weren't violent extremists.
The reasons for the CIA's interest in Oswald prior to the assassination are less clear and should be investigated further...