I haven't been on White Island myself but I took some visitors there a few years ago. I think it is safe to say that most tourists who go want the adventure of being up close to a volcano but not the risk of actually being caught by an eruption. They regard it as something similar to a scary roller-coaster ride or a bungee jump - pretend danger that gives a thrill without any cost. People who venture onto White Island don't expect it to erupt. In that regard they are misinformed, either through ignorance or misleading information. I know my friends (and I) never would have expected such a thing. In a case like this, I don't think the victims reasonably could have been expected to understand the risk. If there are businesses offering guided tours, you would probably assume they must know what they are doing. My thoughts go out to the victims and I don't think they can be blamed for not knowing better. That responsibility lies with the tour promoters.