Economists know this because money stable in value needs to be able to expand and contract with its underlying economy.
There is no single group of economists with a single _opinion_. Economics is a social science, most of the predictions are not falsifiable. A lot of economists drive the agenda of their masters. A good example for successfully using economics as a weapon is Ken Rogoff. A very good example of a failing economic model can be currently seen in india.
timeo oeconomicus et dona ferentes
no. non bitcoiner economists will tell you the same thing, to have a stable value a money need to be able to contract and expand. Your lack of knowledge on the subject doesn't change that.
And economic proposals are falsifiable now. You put them to the bitcoin network and if they are accepted then they are rational. I don't expect you to understand because you just suggest economics isn't a science. I don't think you know what science is.
Next.