Of course, as with all doctrines, there are different versions, but we'll stick with the basic concept - that Jesus died for our sins once and for all. This might not sound like a big deal, but the implications are that sin is no longer an issue, we are always "saved" and are free to live in a state of constant love and approval by God.
As an ex-fundamentalist I found the idea the only thing that made any sense. There were far too many holes in christian logic and reasoning, and the mentality of most christians I found to be one of wilful ignorance based on fear.
The problem with this doctrine however is it requires us to rethink parts of the bible and how we interpret them. This has caused division and cries of heresy (of course) as people immediately forget the struggles of guys like Luther.
In the end, traditional christians can't handle the new doctrines because they are too good. They make a mockery of centuries of self sacrifice in an effort to be holy. It destroys the need for obedience to "the law". It negates the desperate cries for annointings and favour from God. In general, it creates havoc with nearly all traditional doctrines other than the basic idea that Jesus died for our sins. Beyond that, everything is up for grabs!
The big danger however, is that the grace movement leads us straight out the door of christianity forever! And that, my friends, is as it should be!
Christianity became superfluous, simply because apparently Jesus fixed up everything for everyone for all time, so nothing to bother about! From there it was an easy step to seeing that it was all ridiculous - centuries of manipulating a religion to make it work. And work it did!! It hit a niche spot in our psyche that cried for acceptance from a higher power, to find meaning and purpose. It worked like magic as it supplied a scapegoat saviour who fixed up everything for us as long as we obeyed the rules.
At that point, the entire structure crumbled for me. The emperor really had no clothes. We were all walking naked down the street, with those who had the eyes to see, laughing at our gullibility.
Sooo yeah, as I often say, I understand the needs that Christianity meets in so many, but for many of us it becomes redundant - just another religion that provides one perspective on the issues of life. Sure, you can pull gems of wisdom from the bible, and many christian "mystics" have helped us see greater truths that keep the ball rolling.
But its time to grow up. Not in an arrogant way that says I'm right/better and you're wrong/stupid. But in the simple fact that we are far bigger and better than any one religion, and its time for us to look beyond the narrow confines of ALL religions and begin the real journey of life and love.