I think the not-quite-canon Portable Ops did the idea of "words that kill" much better with Gene.

I was really expecting with the whole theme there would be more disinformation, propaganda, narrative control, persuasion techniques type stuff - "words that kill" being the words that turn men into soldiers and killers or cause people to turn on each other in civil war (yes, it's not a materialist understanding of how that works IRL but still). Skullface would be like Gene, a master of controlling words to control the world - if it then turned out his goal was to wipe out the English language: fantastic, that's Metal Gear baby. But instead, the "words that kill" are just the sounds that activate a particular strain of vocal cord parasite to cause a lethal infection. And the same parasites explain all the crazy supernatural powers of the Cobras that didn't need explaining. Combined with all the other unfinished storylines and missing content, it really left me feeling...

Bonus: Gene's speech in Japanese, as voiced by the inimitable Norio Wakamoto