[zAy0LfpBZLC8mAC]

There are two obvious objections to that:

1. If a person is uninformed about the consequences of their decision and the alternatives that they could choose from, is that a voluntary decision? I think it would be very difficult to actually defend the position that the majority of software users decide voluntarily to use proprietary software.

Sure, if someone voluntarily buys cigarettes and smokes, I guess they should be free to do so as well. From that it does not follow that you shouldn't object to cigarettes existing (and in particular to them being offered by vendors to the unsuspecting public).

2. Economists know a concept they call externalities. Those are effects that one's economic transactions have on parties not involved in the transactions, like, for example, pollution of the environment that other people live in. Non-free software very often has negative externalities, in particular due to network effects that lead to de-facto monopolies and lock-in. Negative externalities are a good reason to object to what other people decide to do voluntarily.