You can bury your head in the sand all you want and pretend that criminals actively committing crimes aren't caught every single day during "routine" traffic stops in this country, but the fact is, they are. Uniform Crime Statistic Reports are available in every state, and federally. If only one police officer in this country in the last 20 years was killed or assaulted in the line of duty during a "routine" traffic stop, your argument may have had a little weight. The facts, however, directly contradict you. The fact is that a lot of cops every single year are killed, permanently disabled, or otherwise injured during "routine" traffic stops, by the occupants of those vehicles. There is no reason that a cop on the street shouldn't take precautions to keep themselves safe.
Like I previously suggested, head over to your local precinct and see if you can ride along. San Diego PD is a fairly busy Dept. Also take a look at the Officer Down memorial page on the web.