Depends. Do you value the worth of your activity purely by personal income gained and count every minute in dollars? (Ah, you're a lawyer. Ignore that question.) In many of the cases we're talking about, the faithful employee's long-term reward is achieving things they could never have attained on their own.
> it takes laws to do that and laws restrict freedom.
Yes, the freedom to abuse employees, in this case. Restrict away.
> do tech professionals really want to be prohibited from making such choices for themselves?
Painting this as a choice is wholly disingenuous. If "the 40hr week is forever gone", in what sense is it a choice to work those hours?
> Trying to "bring back" the 40-hour week from this perspective is, in my view, a very bad idea that would seriously harm the tech-driven companies that populate the startup world.
This scaremongering is, in my view, yet more of the short-sighted knee-jerk sky-will-fall nonsense employers always trot out when employee rights are discussed. Which is a) never borne out by the results when the rights are enforced and b) why they have to be enforced.