Dear Mr. Glesser:
Yours is an unusual dilemma. It shouldn't be but it is. Basically it is this: Is it okay to coopt the ideas of others--even if it's legal, and even if you offer slight modifications or even improvements--because you can, and because the originators of the ideas you seek to coopt lack the money to hire the legal clout to prevent you from doing so?
I've actually attempted to write you a thoughtful response twice before, but I ended up deleting those attempts. The issue is deliciously complex, and it was too late at night for me to do justice to the ethical conundrum you pose. I'm going to try to take another crack at it now.
One of the lovely things about a quality, innovative knife manufacturer is that the enterprise straddles the fence between art and commerce. Still, most businesses--the auto industry immediately comes to mind--are me-too businesses. Everyone imitates everyone else. If something proves popular, everyone instantly copies it. Their lawyers sort everything out.
But the auto industry is a mass market industry. The knife business is a cottage industry. When you coopt the ideas of others, it's not really like Ford stealing--excuse me, copying from--from Toyota. It's more personal. In the case of Spyderco creating a new assisted-opening knife based on the ideas of Ken Onion, it's more like Sal Glesser personally taking something from Ken Onion, whether Ken Onion approves of this or not. Ken Onion isn't a mega-corporation. He's just a person. If Spyderco creates a knife that employs a Ken Onion idea, which Ken Onion doesn't have the legal power to protect, it ultimately translates into potential lost sales for Ken Onion designs.
Is this kosher? Well, that depends. The quick and dirty answer is Yes, because everyone does it, and it's legally sanctioned to do it, as long as the appropriate fees are paid for the use of "prior art," as patent attorneys like to say. It's legal, but is it ethical? That's a more difficult and complex question.
But you've already answered it: it isn't. It isn't because you feel it isn't. It isn't because you raise it as an issue in the first place when many others would not. That, ultimately, is the meaning of ethics. Ethics isn't something your church or synagogue says is okay. Or what the government says is okay. Or what your friends and loved ones say is okay. It's what your soul tells you is okay. Your soul appears to be telling you it isn't okay. Even though the issue isn't clear-cut, even though business and legal considerations would put you entirely in the right, the fact that you wrestle with this dilemma suggests that, for you, it isn't okay. The rest is just rationalizing.
Perhaps you are thinking about how you felt when others in the knife industry began to copy the Spyderhole, or the Spyderedge, or some of your knife designs. This is a legitimate baseline for guiding your future behavior. "Do unto others" is one of the Ten Commandments. It's a pretty good one.
In the art world, artists copy each other all the time. In cubisim, Bracque copied Picasso (or was it the other way around, or did they both more or less invent the same artistic style simultaneously?). Picasso and Bracque were friends. They didn't see themselves as enemies or even competitors. And both hoped to sell their work for as much money as possible. But neither was in the business of mass production. (Well, in Picasso's case, perhaps not.)
Mass production is about making money. It's about market share. It's about zero sum solutions: in order for me to win, you must lose. In order for me to sell a profitable number of knives based on a Ken Onion design, I must lure potential customers of Ken Onion's away from his knives to mine.
Is this ethical? Yes! Such imitation is at the very heart of international commerce. Unless someone like you arbitrarily draws a line in the sand and says, in effect: No! I will only create knife designs that employ technological innovations that I have commissioned.
Take the karambit, about which I have done much meditating of late (see my thread, which has over a thousand views: "Spyderco Karambit: Full of Surprises"). The karambit design is old if not ancient. Jay Tarani introduced and popularized it in the US. Ernest Emerson created what is probably the hottest karambit now on the market. Spyderco's entry comes a bit late in the game. But do any of these karambits involve any technological innovations? No, they don't. There are design differences, of course, but a karambit is still a karambit, regardless of the manufacturer.
This is not the case when you incorporate the Ken Onion speed-assist mechanism into a Spyderco knife. It isn't a centuries-old, traditional design. It isn't one mega-corporation laying broad sword upon armor of another mega-corporation. It's Sal Glesser squaring off against Ken Onion.
This is something unique to the whole knife-using enterprise: unlike shooting someone at a distance with a firearm, wielding a knife is a personal, intimate, close-order thing. When you cut someone, your hand is attached to the other end of the cut. There is no distance. Being a successful company like Spyderco affords that distance. You don't need to cut a Ken Onion with a knife. You can, in effect, shoot him with lawyers. You're a company with clout. He's just a person.
Psychonanalysts have an axiom: everything you know is true. There are no accidents. If you want to produce Spyderco's version of a Ken Onion speed-assisted knife, there is nothing in the American way of doing business to prevent you from doing so. The fact that you have reservations about it is, from an ethical perspective, your answer. Ethics come from the gut. No one call tell you what's right. Only you can. It is, in a way, an awful knowledge. It's bad for business. It goes against your interests. But, in the end, there it is.
Neil Chesanow (aka hotwriter)
(As an aside, the first time I played with it I thought it was gonna leave my hand. I love its Warncliffe blade and it continues to be a "keeper.") The button activated switchblade, of which my 9050AFO is an example, is very effective for gloved handed SAR personnel, but is of a design class that has legal implications. 
),
It survived the jump. I'll stick to my Delica for edc.