You need to read the quote more closely

> Libertarians generally believe that voluntary slavery is a contradiction in terms.

In otherwords, they don't believe there is such a thing as "voluntary slavery". That is, if you volunteer for it, it's not slavery. That's a cute word game they are playing just so they don't have to accept the fact that they condone slavery.

A Libertarian supports the idea a person could sign a contract where they get no pay AND they have to follow all the rules of their employer. IE, Indentured Servitude [1]

That's the more direct form of slavery. There is also indirect forms of slavery such as the Company town. [2] Again, if you are following the core libertarian notion that the only thing that government should enforce is contracts between people, then there's nothing wrong with a company buying a city and forcing the inhabitants to use their currency and pay them rent.

> Of course, libertarians believe no such thing and indeed your own link refutes your claim.

No, it doesn't. It tries to hand wave why a minimum wage is actually bad and someone not being paid could be good. A core of the article is this

> The real reason that the minimum wage is wrong is because the government should possess no authority to interfere with the employer/employee wage agreement or contract.

That's a fairly uncontroversial statement for libertarians and one that leads DIRECTLY to serfdom and slavery. But they don't want to take it to it's logical (and historical) conclusion so instead they say "Oh, well, slavery only means forced slavery and NOTHING ELSE".

> At a minimum, virtually all libertarians believe in regulation against (involuntary) slavery

And isn't that a problem? The fact that a political ideology could support voluntary slavery doesn't make it a good one. The fact that the ideology MUST play word games to feel better about itself is also not a good one.

> theft, assault, etc,

I never said libertarians were against personal injury. Though, they'd take it not in the form of regulations but rather a strict injury notion. IE, you don't need a law to say "thou shalt not steal" instead, a libritarian would have a judge say "Without a contract, you took x from someone, therefore you need to compensate them x". These are not regulations. Regulations are things like "buildings may not be more than x height in this area" or "Employers must pay a minimum wage".

> "voluntary slavery" is illiberal and thus subject to regulation (and from the tone of that Wikipedia quote, it sounds like many "except certain right-libertarians" do hold this view).

I honestly think you misread that wiki qoute. It is not saying that voluntary slavery is illiberal, but rather just not a thing. The words contradict and thus make not sense. The further right libertarians are arguing for involuntary slavery. Generally of the form of "I and my family will work for you for 5 generations if you give us Y". The 3rd generation did not volunteer for that. That is what libertarians debate on whether or not it is slavery (with most being against it for obvious reasons).

In otherwords, libertarians argue that slavery isn't slavery when the person signs a contracts willingly. In that case it's just signing a contract. [3]

[1] https://en.wikipedia.org/wiki/Indentured_servitude

[2] https://en.wikipedia.org/wiki/Company_town

[3] https://www.reddit.com/r/Libertarian/comments/34vqo6/change_...