I think most of us can and are more than willing. Iron man for example is good adaptation that modernized the material quit well actually. Spider-man for some reason to me seems a little stuck in the past but whatever.
But as someone said in the Iron man thread, it is interesting how when a movie is good, it usually is said to be pretty faithful if not neccesarily on the surface. But when the movie is considered bad, all of the sudden the film treats the source material like crap.
I think a lot of times some people love the source material so much that they seem to forget that it isn't always great, no matter what decade and no matter what medium. Take the clone saga for example, some people just think it plain sucks, others think it has potential. And yet Ultimate Spider-man tried it again and it still kind of sucked. Some stories just aren't meant to be and could be done on screen perfectly faithful and still suck.
I think the film makers felt they needed to add something to Sandman for example. Which I don't think was neccesarily a bad thing, they just sort of tried too hard to make him more interesting. But I don't really think a lot of people would argue that having him be just a petty thug would have made him anymore compelling, even if it technically was more faithful.
So in the end we can all accept changes. It's just interesting what people get upset over. If a character looks great but sacrifices some characterization fans think it sucks. If the characterization is spot on but looks lame, then it still sucks. Its no wonder these movies are so hard to make.