Utilitarianism and voluntaryism are quite often seen as being in opposition with each other. I don't think that it is necessarily so, which is a topic for another day, but the common view is that they are.
A thought experiment comes up quite often when discussing utilitarianism and I'd like to look more closely at it. This is the experiment: Suppose that a train is bearing down on a group of four people stuck on the tracks. It is certain that they will die if the train hits them, however it is possible to obstruct the train by pushing someone in front of it. Is it right to sacrifice the one person in order to save the four?
The utilitarian answer would typically be yes, since saving the lives of four is serving the greater good. My voluntaryist answer is no, and hopefully I can explain why. First, let's assume away all of the problems with the experiment such as why it's not an option for me to push myself in the train's path and a lack of perfect knowledge (can we really be certain the train will be stopped? Are the four people there by choice? Is the one life a potential Ghandi and the four potential Hitlers? etc.) Even without all of those flaws, I can't see myself ever choosing the kill the one.
My reasoning is both simple and complex. The reason I couldn't make that choice is because it wasn't my decision to put the four on a collision course with the train, but it would be my decision to sacrifice the one. I cannot through my own actions bring an innocent to harm, even if it means ending the harm to other innocents. Let's face it, the whole situation is tragic and that can't be corrected, and I can't possibly weigh the good done to the four against the evil done to the one, I don't think the scales are even compatible let alone measurable. The calculus is far to cold for me to make.
Also, once one is able to rationalize this decision, it becomes much easier to rationalize decisions that are much more grey. This sounds like a slippery slope argument, and I've never been fond of them, but it's more nuanced than that. Everyone has to draw a line in the sand somewhere, and to me this line is much more clear and easy to avoid crossing than pretty much anywhere else it could be drawn. It is unambiguous and not arbitrary. Once you start basing your line on the relative value of people and situations, it gets messy really quick and too easy to draw that line in the wrong place.
The thought experiment aside, the real world isn't going to present such clear cut scenarios. There will always be a great deal of uncertainty as a part of every decision. The utilitarian line in the sand requires a level of knowledge which is just not attainable, and it also requires a person free from biasing emotions. I am both without perfect knowledge and affected by my emotions, and that makes the clear line in the sand all that much more important.
If the person on the plaform chooses to sacrifice himself for the four, then I would be willing to assist him in stopping the train, but I won't be forcing him to do it. I always know on which side of the line I'm standing, and that's better than guessing that I've got it right.