As I clearly said, and as I demonstrated in the links I provided, their portrayal has varied over the decades -- obviously, since they've been written and edited by many different people over generations in which the standards of comics have changed. I'm not saying they've never killed, I'm saying they haven't been portrayed exclusively and consistently as killers. You're focusing on their origins and their recent portrayals, but that disregards the decades in between when comics came to be aimed more at children and the Comics Code Authority placed severe restrictions on violent content. To believe that superheroes have been consistently and unvaryingly portrayed in a single way in the 50-70-some years since their creation is unrealistic in the extreme. The very nature of superhero literature is its mutability. Many characters have been portrayed as everything from dark and gritty casual killers to ultra-clean-cut, child-friendly paragons of virtue. You can't pick one single portrayal and insist it's the only one that exists. There is a choice in the matter.
Cases in point: The Ben Affleck Daredevil movie portrayed him as a deadly vigilante who came to question his violence and ended up choosing not to kill the Kingpin, but the MCU Daredevil is portrayed as a vigilante who almost invariably refuses to use deadly force. The MCU Hulk is portrayed as willing to kill, but the Bill Bixby/Lou Ferrigno version was emphatically established as a non-killer -- both portrayals being consistent with the contemporary depictions in the comics. The Burton and Snyder versions of Batman are killers, but the Nolan version at least nominally refused to kill (though the movies were inconsistent and somewhat hypocritical in their depiction of that refusal), and most comics and animated incarnations of Batman since the mid-1940s have given him an inflexible code against killing. (Even Frank Miller's Dark Knight Returns Batman wasn't a killer. "Rubber bullets. Honest.")
Yes, the earliest comics showed Batman and even Superman as routine killers, but that was the influence of the pulp literature they were derived from. The medium evolved over time due to many influences, and the popularity of comics among children led to a tighter rein on violence, leading to more moral and nonlethal heroes. That standard endured in comics throughout the '50s, '60s, and '70s, so characters from that time (such as the Fantastic Four and Spider-Man) often had clearly stated policies against deadly force, even toward their worst enemies. Even Wolverine wasn't nearly as violent at the start as he became later in the '70s and '80s, as the trend started to reverse itself and more deadly characters began to appear. But many of the characters from that era have retained their no-kill policies even as other, deadlier heroes have emerged around them. Spider-Man is one of the most adamant non-killers; I recall an arc in Dan Slott's ongoing run from a few years ago where Spidey decided that he would not allow anyone, good or bad, to die in his presence if he could help it. Later, when his body was taken over by Dr. Octopus for an extended story arc, the "Superior Spider-Man"'s willingness to use lethal force was shocking to his friends and allies and led to some serious questioning of his sanity and identity by the Avengers, since killing is so massively out of character for Spider-Man (although a few of the Avengers, like Wolverine, were fine with him crossing that line).
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