X% of surveyed economists probably don't disagree that rent controls will have the effect that rent control proponents claim. They likely believe it will have other effects in addition, and that these other effects are, in aggregate, worse than what benefits might also be offered.
Rent control proponents believe that imposing rent control will lower rents. With the goal of making housing more affordable. Economists know that it will benefit a few but in the process reduce supply and therefore increase average rents. Creating the very problem that you're trying to solve.
By contrast, advocates for rent control probably don't believe that the economists are just making stuff up - they just believe that the downsides of the stuff the economists are talking about are less than the upsides of rent control.
That doesn't match my experience. It is not that advocates for rent control believe that rent control is a net positive despite what economists say. They actively do not believe that rent control reduces supply and increases average prices.
That has held true in both position papers and personal conversations that I've had with people.
Tangentially related. In research, learning positive facts about something makes negative facts harder to remember. And vice versa. This cognitive quirk helps explain why it is hard for people in general to believe that there really are downsides to the things that they support.