The phrase "unwarranted assumptions" means making beliefs or conclusions without enough evidence or justification. It refers to thinking or accepting something as true without proper reason or proof. Full definition
I'm not a climate scientist, but, as a social scientist, anthropologist and semiotician, I do have many years of experience with colleagues making unwarranted assumptions based on ignorance of certain fundamental scientific principles. (judithcurry.com)
To a manager making unwarranted assumptions about his or her ability to monitor employees, a dysfunctional performance measurement system looks just fine — measures are increasing. (sciencemag.org)
That'd be a lot more useful than adding up how many lawyers use the firm's stationery, and drawing unwarranted assumptions from the result. (slaw.ca)