I've spent my entire life in the Christian community, but I've never been too comfortable with guerilla evangelism tactics. By this I mean deliberate rhetorical simplifications or shortcuts that force people to verbally accept the Gospel before they know what it is, or regardless of whether they want to accept it. A classic example would be the altar call for children: "If you don't want to burn forever in Hell, let Jesus into your heart and you can play forever in Heaven." That's guerilla evangelism. No child in their right mind would turn it down. A decade or two later, Christians are baffled by the decline of church attendance and the trend of disillusionment with the faith — but how could you expect anything else from such a vapid, non-refutable presentation of the faith?
Another example would be the essential Ray Comfort line, "Have you ever lied? Have you ever stolen? Well, that doesn't just mean lying and stealing are things you've done — that means you're a regular liar and thief. Thus, if you don't want to burn forever in hell…" etc. A friend of mine recently inverted this cliché over lunch and asked me, "Have you ever been kind? Have you ever done a good thing? Well, that doesn't mean kindness and goodness are things you've done — that means you're a regular do-gooder through and through." He exposed the nonsense of so recklessly conflating what you do with what you are.
My beef isn't necessarily the point behind the line, but the posture of the line itself. The point of the line is that our faulty actions can only be explained by faulty ontology — an idea that society does support for certain crimes. Once you have murdered, you are a murderer, and no one would say you can un-become a murderer. That label follows you for the rest of your life. The same goes for rape, molestation, and other particularly weighty crimes. There are no "former murderers" and "former rapists" — only murderers and rapists. A check-box on a job application might ask you if you have ever been convicted of a felony, regardless of how you have changed since committing that felony. Some crimes immediately overtake your identity.
Some crimes don't. A person who tells white lies is not certainly not considered a liar for life. Neither is a child who steals from the cookie jar considered a thief for life. Both of these figures could be a liar or a thief at one point in time, but to stick that label to them later in life seems harsh. The same goes for recovering alcoholics, gamblers, drug addicts, and so on — while you can't be a former murderer, you can be a former alcoholic. Below these are crimes that don't even leave a footprint. Cheating in high school doesn't usually make people call you a "former cheater." Neither does a period of lying make you a "former liar." You did these things, and now you don't.
Why do these distinctions exist? Part of it has to do with how severe the consequences of an action are. Murder has serious impacts on family, economy, and community in a way that an insincere compliment of someone's haircut doesn't. A related factor is how prevalent the action is; for instance, enough people have cheated academically in various degrees to the point that labeling all such people as cheaters for life would be moot. It might even make society less productive.
That being said, questions of consequence never really get around to whether or not an action is ontologically good, which is what the original guerilla evangelism line is clumsily trying to get at. The reason we have inescapable labels like "murderer" is that we do understand the broken ontology of the human condition, if perhaps too selectively. We feel most comfortable dodging for ourselves the labels we put on others; from a broader perspective, maybe it is true that we are all liars and thieves. Or maybe it isn't. That's what discussion and nuance are here for.
Personally, I do consider myself a liar and a thief, but not because Ray Comfort required me to say it in front of a camera. I believe in a broken ontology because it has been the starting point for healing and redemption in Christ. It is the relief that I do not have to fix myself or work for salvation. It is allowing God the work of and credit for renewing my life.
Perhaps you don't consider yourself a thieving liar, and that's okay. Don't let intimidating rhetoric bully you into a position; weigh the sides, test what you can, and seek how best to live in all situations. Peace.