So basically christians can do what they want because their sins, past, present and future are all forgiven?

i have heard this from more than one christian that no matter what he does he will go to heaven because he believes in jesus and is saved...he is a very violent x- convict, but he attends all the chapel services here at the homeless shelter...and is the first one to yell out, amen and alleluia...but 10 minutes after the service these christians are ready to kill each other...and listening to some of these preachers, i can their point...(of course it is a freaking stupid point)