It shouldn't matter if it's someone's pet project, everyone needs to openly and honestly challenge assumptions, but in a structured way (i.e. using PowerMaps) so learning can be accelerated and action can be taken BEFORE more resources are poured into it. But note: any form of retribution against someone for challenging assumptions is a deadly sin that will harm your company by making it more stupid, weaker and easier prey for predators in your industry who aren't afraid to challenge the status quo.