There is a ubiquitous pleasantry afoot, which seems to have replaced "you're welcome" as a response to "thank you," and that's No problem. It's mildly annoying. It implies that the whole transaction could well be viewed as a "problem" but for the incredible generosity and kindness of the utterer of "No problem."
A problem, etymologically speaking, is something that is thrown forth -- something troubling and unclear that one must confront, a conundrum or perplexity that needs unraveling. We are, I suppose, on some levels, all problems to one another, ciphers, riddles, loci of babbling unclarity, texts to be translated.
Communication is vexing and fraught, especially to those of us whose neuronal fight-or-flight systems are congenitally in overdrive and who are perpetually at risk of tranmogrifying into Travis Bickel asking our mirror image You talkin' to me ???
"You're welcome," on the other hand, cuts through the problem problem. Hospitality replies to gratitude; it's practically an exchange of lovers.
There are moments, though, when the problem, the capital P Problem, of self and other and of self and world, seems to unravel, even disappear.
And all that is left is "No problem,"
gratitude and welcome everywhere.