You smile and say, "I appreciate your input. I value it and consider it a good starting point. I am not certain it alone provides the level of support necessary for me to consider a different path, but I would consider both additional data and reducing the amount of evidence I require with a good reason."
Like everyone else, scientists are so convinced of what they know that they won't listen to other opinions.
The problem is that scientists think their knowledge is truth because it comes from "the scientific method." They fail to internalize that the whole point of that method is that no knowledge is sacred and everything should be doubted to the degree at which evidence exists to the contrary.
A crackpot conspiracy theory with a single anecdotal source of data is sufficient to create doubt in the soundest of theories. Just not much.