i like ingrate's answer, and i wanted to take a stab myself.
perhaps my interpretation of the question is overly simplistic, but as i understand the term "voluntarism", it essentially means "acting without coercion of any sort". seems pretty anarchistic to me. although, as ingrate pointed out, coercion comes in many flavors and levels of obfuscation.
in the explanation, several questions are raised that point to the voluntarism of others. if someone chooses to put/keep themselves in a situation where they are being oppressed, i would surely - assuming that person or situation had some relevance to my own life - at least try to understand why they have chosen to do so. maybe they don't see that situation as oppressive, although i do; i would probably try to talk to them and see why our perspectives are so divergent. maybe they see the situation as somewhat oppressive, but less so than whatever they see as their other options; i would try to understand what their other options are (maybe they are right).
in any case; if they choose to be in that situation, even after i have satisfied myself that they understand all of their options, i would not likely intervene.
2 very common (unfortunately) types of situation like this are: folks in abusive relationships, and folks in oppressive "work" situations. i'm sure we've all seen this up close. most often, i hear the explanation that "i have no viable alternatives that are better". while i may see some pretty obvious alternatives, they don't see it that way. if we have the opportunity to discuss the situations and alternatives at length, maybe they will see something they previously didn't, or maybe they won't. in almost every case, i will defer to their own desires. this world creates/enables some pretty fucked up shit, but i can't "save" anybody. that is their choice.
however, i must confess that when i was a late teen, i came precariously close to killing someone that was being violently abusive to a female friend that i had a major crush on. even though we had talked about it at length, she made it clear that she would not leave the guy ("the good outweighs the bad"), and did not want any interference. i chose to confront him on it anyway (growing up on the inner city streets of nyc - back in the 70s - definitely infused me with a bit of the machismo that was so prevalent in the newyorican culture that i was immersed in), first verbally and then physically. when he stopped coming around the neighborhood - coincidentally at the same time that he suffered some major injuries - she swore she would never forgive me. she eventually did, but ironically not until her mother was killed by he drunken boyfriend, several years later.