And of course startup founders benefit from positive externality of others. In the case of employees, they have defined and agreed upon compensation.
In the case of medical research, you will benefit from $1 billion for a set period of time, before you lose exclusive rights to a drug and anyone can benefit from it. Then your drug contributes to the 95% of hard work for someone else's drug.
I think you actually turn around your argument in the last sentence. It seems to me you start arguing against inheritance taxes because then people will stop trying to get rich, unless what you want is for everyone to not be rich ("touching the gains" from your first sentence). If people have nothing to gain and everything to lose, since they can't get rich and they risk being destitute and broken, then for what reason will society continue to function? Society won't function, it will devolve into various groups jealously guarding arable land and water.
The issue is, will higher taxes (not 100% taxes) on income and wealth stop entrepreneurial activity? I don't think so. Is someone going to quit because they'll pay capital gains of 30% instead of 20%? Doubtful.
The issue is what is the appropriate taxation level, not whether it should be 0 or 100%. Currently, most debates devolve down into extremist scenarios that no one is proposing.
I think that quote is here:
http://www.businessinsider.com/warren-buffett-taxes-2011-8?o...
This is like saying "ok, there was a bug in World of Warcraft, that allowed a bunch of sophisticated people to level up unfairly. We've now fixed the bug, and the same is meritocratic now. However, we will not be taxing or nerfing any of the items that got duped or hacked by those who took advantage of the game flaws previously."
Saying you can't draw a line or make a definition is a fallacy. As a society, we can draw any lines we want, and what is just or ethical is defined by society. Imagine we didn't have any speed limits, would your argument be "it is impossible to define an appropriate speed limit, since the right speed limit varies by road condition, traffic, weather, etc. Is it 60 mph, or 62.49 mph? Since we can't come up with a scientific rule for this that holds, we may as well have no limit."
I'd go further and said the idea of defining the concept of "saying whatever they own and made justly" is flawed. What startup founder hasn't benefited from positive externality of others? If you invent a new drug, that is based on an insight you had reading a university journal, from a publicly financed university research center, and you make $1 billion on this insight, even though 95% of the hardc work was done by research scientists publishing openly, do you deserve to pocket this entire $1 billion while everyone else shoulders the burden of paying for the public research?
Is it too hard to just ask people not to be greedy douchebags who try to defend their earnings from a lottery ticket with libertarian philosophy, and just accept that success in this society, especially entrepreneurial success, is a complex function of many variables, only one of which is hard work, or intelligence, or coding skill? And that there are other huge pieces: your social network, your friends, where you were born, timing and plain old luck, and that it would be better to encourage a continuance of this lottery game, if more people had the resources to do it, and a social safety net to tolerate failure?
As Warren Buffet said (paraphrased), an entrepreneur isn't going to stop trying to get rich because of a 10 or 20% hike in marginal or capital gains taxes. That's absurd.
People will stop trying to get rich, if they don't have family with savings or capital to fall back on, and in which a failure will leave them destitute and broken.