ID puzzle

Coming from a country where it’s mandatory for me to have an ID with myself (Germany), but where I’m pretty much never asked to show it (often, not even when crossing borders, and certainly not when just taking some long-distance train), it’s a remarkable contrast to be in the US: Here, the national ID card seems to be a major political scarecrow — yet, I’ve never seen as many demands for “showing ID” as in the past 10 days in New England. Want to buy alcohol or tobacco? “Take it as a compliment — we ask for ID on every purchase of age controlled goods,” says a sign in the shop. Want to pay a relatively minor purchase by credit card? “Could I see your ID?”I find the discrepancy puzzling between, on the one hand, ubiquitous use of ID, and on the other hand, massive fears of the adverse effects that a national ID might have on privacy.