It is so easy being designated as the one who just says “No!” to everything and whose largest contribution to the team is to foster a negative energy in every room you enter. But have you ever thought about how these people may actually be trying to do something completely different and of immense value?
If you think they are assuming that your project will fail, maybe they are just trying to see the warning signs ahead of time to let you know where to look again, make changes – and ultimately succeed? Maybe they are just as invested in your common success as you are?
There is actually a term for it in project terms: Doing a pre-mortem; assuming that the project has just died and then work your way backwards from there in order to find the risks, you should see and address before it is to late. Given how many projects fail, maybe it is an exercise worth remembering?