Alright, I've had about enough. The flawed logic of these comments are really starting to shit me. You know the ones I'm talking about: "I'm no angel, but there's nothing wrong with being a 16 year old single mother who pays her way by working in the sex industry.", "I'm sure none of us are saints. So what if I killed a few hobos? It was all in good fun", "I encounter many teenage deaths, and let me tell you, it's no fun putting a teenager into a body bag". They use unrealistic expectations to show that no one can meet them.
What exactly am I talking about? Well, let's look at the first example. Putting moral relativism aside, let's assume that 16 year old single mothers who work in the sex industry are skanky hoes and skanky hoes are bad for society. The statement "I'm no angel..." is supposed to imply that no one can stand up to an uncompromising moral edifice. This is fine in itself. After all, these expectations can be rather high, even to what most would agree are 'good people'. The extended implication, however, and the issue I have with the statement (and indeed, the attitude), is that because no one can live up to these unreasonably high expectations, that absolves the speaker (also unable to live up to these expectations) of any moral wrongdoing.
The point is very effective when spoken to the layman. It lays doubt not only on unreasonable expectations, but on expectation as a whole. After all, where would one draw the line (indeed, for those that disagree, they could be called upon to draw a line between what is acceptable and unacceptable, something which is quite difficult to the everyman). No matter what this set of expectations is, someone (in the audience or otherwise) would not meet them, despite their being 'good people'. Therefore, expectation is "shown" to be an unrealistic, and untenable model, which in turn answers their moral questionability (ie: one cannot question morality without any grounds).
Before I go on, allow me to put my final statement "it's no fun putting a teenager into a bodybag" into the fold. This statement is not actually designed to absolve the speaker of any wrongdoing, but is still abusing unrealistic or extreme points of view. At worst, it can lead to the further corruption of the english language. The example that comes up is using the word "literally". It was the case once that it was used to draw emphasis to the fact that what was said was in fact the case: "it was literally
raining frogs!" (meaning that real frogs were actually falling from the non-metaphorical sky). However, it is now the case that "literally" is often used to add emphasis without exception: "We were literally
drowning in our own sweat." (meaning that we were metaphorically drowning in our own sweat, but there was still a lot of sweat). Clearly this is abhorrent, and further instances of this abuse must be avoided.
After all, it isn't as if someone's going to say: "It's no fun putting a teenager into a body bag? Well shit, I learnt something today. I mean, I'm a teenager, and I was going to kill myself for the entertainment of the paramedics, but now that I know...". My point is that if you have a pretty much causally true statement at hand (something that often happens when comparing extremes), there's probably no need to say it.
Anyhow, let's return to the matter at hand. The arguement is actually pretty water-tight (in a social setting. The logic is flawed, but this won't stop the speaker from saying it or the listener from believing it). No one will be able to draw a clear, black and white moral line, and no one will be able to defend his or her own decisions in life to unending scrutiny. This leaves the reasonable person at a loss. They cannot show the logic to be false, since there doesn't seem to be anything wrong with it, nor can they then put any other expectations on the speaker. The speaker can draw arbitrary rules at a whim, without being questioned -- moral relativism.
While I can't think of a way to answer this, I'm sure one exists.
 Note that none of these are actual quotes, but I'm sure you've all heard something like it.
 I've used the terms "false logic" here, but this statement is not strictly correct, since I haven't really proven the logic to be incorrect. The logical procedure is probably fine, but it's a perversion of logic by using extremes, which makes it false.