my experience is, there are lots of people in the world who find it very important not only to have a very clearly (rigidly, even) defined path for themselves, but to enforce that path for everyone else.
but pretty much everyone picks and chooses which rules of their religion they will follow. it's been a few years (er... decades. sheesh.) since i read the new testament, but one thing i remember is that most of the rigidity came from people like paul (who, you'll remember, never actually met jesus. just for the record). jesus himself was a lot less rigid about the rules he followed.
and boy, if i were willing to be a little less respectful of other people's houses of worship, i would SO do some performance art that involved going into one of the megachurches with a bunch of stuff for sale in the lobby, asking out loud, "what *would* jesus do? oh, right!!" and then wrecking the place. but then, i figure if people are going to try to impose their beliefs on me, they darned well better be holding true to their beliefs. but unlike jesus, i'm not willing to go around stirring things up that much.
but the point i was actually trying to make is this: there are people who are all over the map about what and how they believe, and christianity has a really wide range of how people practice it. i grew up going to churches where they disapproved even of reading the narnia books, madeleine l'engle, and susan cooper. probably also tolkein, but i wasn't into those yet. they said those books were un-christian. if you're familiar with the authors, they are actually *deeply* christian, and the christian symbolism in the books is really thinly veiled. but the books also spoke out against the kind of religion that spends more time telling people they are evil than actually doing good in the world.
but i had read those books, and absorbed the (apparently subversive) principles they taught long before my church tried to tell me (and my parents) it was wrong for me to read them. and there was no going back. i couldn't help but prefer a religion where it was more important to listen to the small still voice inside of me than the loud, critical voices speaking from the pulpit.
all of which is to say, i think that done with respect for each other, and from a loving place, there is nothing wrong with ttwd. done in a way that is disrespectful of either party, or that makes them into less of a whole person... that is sinful.
and you can define that for yourself.