Their sin may be forgiven, but they're still sinners, right? They are still capable of sin even after being saved. Just like an alcoholic is always an alcoholic, even if they've been sober for 10 years.
There is a distinction which is sometimes made.
A sinner is one who sins as a matter of course (i.e. he/she is powerless to not commit sin). It is their condition.
OTOH, a christian has been freed or, is in the process of being freed from the power of sin (i.e. the compulsion to sin). The true christian has access to the power to avoid sin and lives to minimize sin in his/her life. They ocassionally do sin, however, the occurrence of sin should decrease as they grow more and more into their christian being.
You can make a comparison to smoking.
Who are the smokers ?
Those who smoke a consistent of cigarettes a day, are content to do so, and, in no way, have any plans to quit smoking ...
... or ...
Those who have committed themselves to eventually giving up smoking completely, ... and, have availed themselves of any the various methods to stop smoking (i.e. the patch, gum, hypnosis, etc.).
Over the course of time, their smoking has decreased, to the point that some can go for substantial periods of time without smoking. However, they still feel the urge to light every now and then, though not so constant as before, ... and, perhaps they will give in and smoke a cigarette or two in their weaker moments.
Yes. Adn the occurence of sin should decrease as they grow.
But this is not always in a linear path, as you seem to think. Ideally, like the smoker, the frequency, duration, and magnitude of the smoking should eventually all diminish.
But we all know people who have quit for some time, only to fall back to smoking as much as they did before. The goal is indeed cessation of all smoking, and this may be acheived for some time. But as long as we are on this earth, we may always fall prey to the vices that we are specially suited for.
SD