There's a big, unbridgeable chasm between calling some folks without M.D.s "doctor" and calling police and TSA "officers".

College professors, chiropractors, D.O.s, and others with years of study and deep knowledge in their fields with the degrees and requisite knowledge to support their insights have earned the respect. They are learned, have spent thousands of their own dollars to acquire their expertise, and readily provide tangible benefits to society on a daily basis. They are also members of professional associations (in most cases, at least) with clearly defined and enforced codes of conduct.

By contrast, a TSA screening clerk need only have a high school diploma or GED (and in some cases doesn't need either). By comparison, these folks are poorly trained, uneducated, and unqualified to provide insights and make judgment calls (hence the TSA SOPs, which the agency insists be followed at all times). In many cases these folks appear to be slow learners; how many times have we heard about people being "retrained" for not understanding or following even simple procedures? (And how hard is it to educated a TDC about Nexus cards and the like - this has been going on for quite some time already.) By comparison to the first group, these people are not (on the average) learned, have not spent thousands of dollars to acquire expertise (DrVry and community college just don't compare here), and do not provide daily tangible benefits to society. From all the reports of crime committed by TS"O"s in and out of uniform, it's clear that there is no professional code of conduct mandated or enforced by TSA.

Police fit into a category that's somewhere in between these two opposites. In many cases I'd say that police have earned the use of a courtesy title - though there are exceptions (mainly those who would be considered to be "bad cops"; you're going to find this in any profession though).