Capital vs Capital
I don't know if Picketty tries to make this distinction. The rest of the world fails badly, and indeed sometimes turns it upside down.
We should distinguish between Good Capital and Bad Capital.
Good Capital is the classic entrepreneur and his/her investors, putting their resources (money, time, effort, etc) into things which are in some way a net benefit. Note that that includes those who work in a productive field and derive an income for their efforts, as well as those who invest their money.
Bad capital is the monopolisation or consumption of the commons: finite and indeed scarce resources. If you own property you can derive huge advantages from it, yet it's a zero-sum game: what I own, you are denied. Furthermore you expect the long-suffering taxpayer to support your monopoly, so If I and my very big mates decide to move in to your house, you'll turn to the police to restore your rights. In other words, people much poorer than you are required to pay to uphold your monopoly.
OK, having a house to live in is not a bad thing, but it's still less deserving of reward than Good Capital (the house being its own reward). But what about the property empire? That weekend home that stands empty most of the time, and could otherwise house some hard-pressed local family? Or to take another case, the destruction of the commons by burning of fossil fuels? These are Bad Capital, in that ownership of them confers no benefits but imposes actual costs on society.
Good capital should be encouraged. Bad capital should be taxed. All too often, our society does the exact opposite.
 Maybe even a more dubious field like writing provocative articles for some dodgy online publication.