You're haivng it both ways, though. You're saying the appeal is partly that he's a killer and so he incurs le Carre's wrath. But that he's not so dissimilar from Leamas because he doesn't always kill. Sure, if he were just a high-flying civil servant nobody would want to be him. He's dangerous, and that's attractive. But very few people want to do that stuff, do they? The appeal is that this is the drink the world's best secret agent drinks. This is the style of a very dangerous man. People aspired to the style because he was also an assassin - but nobody wanted to actually do the assassinating bit.
So you said:
"How many people really want to be James Bond, government assassin, blunt instrument?"
Very few. Bond is a government assassin and blunt instrument and peopl want to be him. But they don't want to be James Bond, government assassin, blunt instrument.
What I THINK I'm trying to say is that Le Carre maintain Bond's appeal is the capitalist dream element. And yet, without being a spy, Bond has no appeal, however well-off, as just a civil servant. And yet, Bond also doesn't always kill, not unlike Leamas. Le Carre's argument, therefore, has little ground.
Conversely, no one (as an aspirant fan) wants to do the killing bit in immitating Bond, fair enough: and yet without the killer element, the ability to be ruthless, save the world etc, Bond is just a well-off guy who has particular tastes. (This is the drink drunk by a posh civil servant, this is the hotel stayed in by a posh civil servant. Ooh.)
So there has to be an appeal in being a killer? Which makes the reader as morally corrupt as Bond. And therefore Le Carre is right.
I think.
