Genuine Question. Why do US Immigration / Customs officers carry sidearms?

You are in a secure area of the airport, interacting with passengers who are arriving on international flights and have been screened for weapons before boarding.

I have traversed through Immigration and Customs in Australia, Singapore, Hong Kong, India and the United States, and the US has so far been the only country where I have been greeted by a Immigration officer carrying a sidearm.

Its fine and dandy to say one should not be physically threatened by a uniformed officer with a holstered sidearm, but people in most of the civilized world who don't see guns very often can and do get intimidated at the sight of a uniformed person bearing firearm. Surely the very first interaction that a foreigner has on US shores can be a little less intimidating.