Does it bother you when you thank someone and the response is an airy "no problem"? This is increasingly common, especially among the younger crowd. As a not-terribly-old adult, I find myself succumbing to the same reflex all too often. But is there really anything wrong with "No problem"?
It's true that it somewhat undercuts the original thanks. Spelled out in full, "thank you" essentially means: "I appreciate you going to the trouble to help me." The response "no problem" expands to: "There's no need to thank me because it was no trouble." The implication is that you may continue to ask for help as long as it remains no trouble, but please piss off if you really do anticipate causing a problem. Compare to the traditional "you're welcome", which says that you are welcome to continue to ask for help when you need to.
Confusion between gratitude and praise may be part of the explanation as well. When praised, it's certainly not impolite to self-deprecatingly deflect the praise somewhat. It can be embarrassing to be praised. But being thanked is not the same thing, and deflection can create the impression that perhaps the gratitude was misplaced. If it really was no problem, why extend thanks at all? We do not thank someone for stopping at a red light.
How do other responses to "thank you" stack up? "My pleasure" is an ambiguous one. It could be taken to mean, "there's no need to thank me because not only was it not a problem, it was actually a pleasure." This goes even beyond "no problem" in its deflection of the gratitude proffered. Or it could mean, "it was my pleasure to serve you," a statement beyond "you're welcome." Then there is "not at all" and "sure thing" and the like, which are essentially along the deflectionary lines of "no problem."
These contemporary social formulae reflect our increasing preference for casualness. It's no longer cool to care greatly about much of anything. "You're welcome" indicates that you cared and appreciated the thanks. "No problem" indicates just the opposite: you're a laid-back fella, for which nothing much is a problem. It was no problem to pass the salt. Oh, you ran over my cat with your car? No problem.
That casualness is the real problem. To digress for a moment, I like the story of the premiere of Stravinsky's Rite of Spring by the Ballets Russes in Paris in 1913. The performance was so radical both musically and choreographically that a riot broke out, so severe that the dancers could not hear the orchestra playing, and police had to intervene to break up fistfights in the aisles. Can anyone imagine such a scene today? Not that I wish for more fighting during music performances, but it would be nice if people cared that much. There was a welcome outburst during the last intermission of a performance of Götterdämmerung I attended a few years ago: some intepid audience members yelled out please not to applaud at the end until the opera was entirely over (rather than applauding over the final few notes, as had happened in the first two acts).
I didn't yell out a "thank you" to them, but I'm pretty sure that if I had, I would not have heard back: "No problem!"