The only justified profit is from personal capital. That's the worker's time expenditure, his skills, knowledge, experience, physical and mental capabilities, etc. This capital offers value to production that the laborer is responsible for, thus deserving of a compensation.
When you profit from something like land simply because you own it, even though your not responsible for the role the land plays in production, the compensation isn't justified.
When something is acquired without justification under threat, it's literal extortion. Since market prices are enforced by law enforcements, the source of threat to pay unjustified market prices is constant. So any unjustified market prices, which profit from impersonal capital all are, are extortion as defined by the law.