It is only hinted at in the book that Marco does that, but he mentions remembering the USA and a General Jorgensen. Jorgensen had committed suicide as a protest against what Senator Iselin was doing, and Marco told his girl friend he would avenge Jorgensen's death. In the book, Marco goes to see Raymond while carrying a pack of cards and it is implied that he used them to reprogramme Raymond. None of the Jorgensen sub-plot is present in the film, in which Raymond finally breaks free. In the book, he never does.
"Chicken soup - with a beep straw."

I don't recall that from the book. I do remember one big difference was that in the book, Marco's interrogation of Raymond happens after Raymond gets his assignment so Marco knows what it is.

In the book, it is hinted that Marco programmed Raymond to shoot the last three people he kills, one of them being himself. Marco is more ruthless in the book, and has more influence on events than in the film. In the film, Marco says Raymond "freed himself at last" as an epitaph at the end but in the book he merely says, "No electric chair for a Medal of Honor man," and there is no suggestion Raymond freed himself, but rather that Marco influenced him via the programming, instead of his mother, so Raymond became Marco's instrument rather than his mother's.
"Chicken soup - with a beep straw."

All witnesses to this Communist plot died when Raymond died, didn't they.
The Communists programmed him that way.
When Raymond said: "Oh God, Ben." was something coming over him urging him to kill himself? I mean, wasn't he proud of what he had done? He put on his Medal of Honor.
But he was told to kill every possible witness to the crime. And Ben Marco was busy running and didn't see him do anything.
The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
E. Burke

Wouldn't all the "programming" disappear when Marco pulled the plug with the loaded deck, and wouldn't Raymond start remembering everything that happened since it was still in his subconscious?
The suicide wasn't about love, in my view, but being overwhelmed with guilt (assuming Raymond wasn't a sociopath to begin with) and possibly facing criminal charges, not only for multiple murders but for treason (even if he wasn't morally responsible for what he did since his free will was compromised by the extensive brainwashing).

But Lt. Marco programmed or "brainwashed" Raymond to forget the death of his wife and her father, Senator Jordan.
I know how nice it is to feel love conquers all, but this movie has nothing to do with loveeven motherly love.
It's about politics and using assassinations to "rally the voters to sweep us up into the White House with powers that make martial law look like anarchy".
There is no room for romance here.
The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
E. Burke

Even if he wasn't morally responsible, Raymond would have to live with the guilt of having personally killed a number of people, including his wife, father-in-law, mother, stepfather, employer, and two fellow soldiers.
It's possible that Raymond would be tried for murder and, if found guilty, face the death penalty.
Suicide, to him, seemed like the only way out.

oh, and in the book Mrs. Iselin was a heroin addict.
The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
E. Burke

It took me forever to figure out that Mrs. Iselin, Raymond's EVIL mother, was actually the only person who could've taken down "and pulled into dirt" American Communists.
Yes she was evil, yes she was a Soviet Collaborator, yes she used her son as her personal sex toy, but she flippedhated the Soviets, and I think she would've been the best person to tear down Communism in America.
Ultimately, the Assassination at the Republican Convention eliminated the Iselins and brought all the attention to the Republican Party as being the Party communists hated the most, and then the surviving candidate and new choice for Vice President could be flipped to the Communist side or maybe were already involved with American Communism.
Raymond assassinated America's hope to eliminate Communismhis evil, incestuous mother and flying monkey husband.
The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
E. Burke

Personally, I believe that he just couldn't live with himself. He had already been "De-Programmed". "Un-Brain Washed"???? Whatever? He knew what he had done. He had reached the end of his tether. Instead of his mother's target he finally did what he felt was right. He shot Mother and Johnny. and since he really didn't care any longer. what point was there to live?
"Fasten your seatbelts. It's going to be a bumpy night"

I think he was programmed that way.
I'm sorry, but you're mistaken. Ben broked his programming.
The louder UFO "debunkers" argue the more terrified they are it's all true.

I think he was programmed that way. When the plot was discovered he was programmed to eliminate all people in the knowincluding himself. A sinister plot indeed. No matter what happens, the communists will achieve their objective.
The only thing necessary for the triumph of evil is for good (wo)men to do nothing.
E. Burke