And let's remember that vandals aren't going to give a rat's arse about markup; you don't need to know what all that gibberish means to replace it all with "u eat poo-poo". But overall, yes, we want good-faith contributors who are willing to expend exactly zero effort learning how things work, because fixing typos will in many cases progress to fixing facts, which may lead to discussion and further involvement.
The point is a low barrier to *entry*. Once you've gotten comfortable with just editing, it's assumed that you might want to start discussing things and learning policies and so on. Or you might not, which is also fine as long as you stay away from anything controversial. You don't need to read Verifiability or Neutral point of view to know that things should be verifiable or neutral; you just need someone to add {{fact}} or {{npov}} or something to a page you edit, once.
But none of this will necessarily happen if you didn't do something to commit yourself first. It's the "foot in the door" principle: people who start small will be more willing to proceed to bigger things than they will be to start out with big things. What were *your* first edits to Wikipedia?