Admitting You're a Sinner

[vulcanlogician]

This analogy doesn't work well.
First, you can lose weight, and that pretty much makes up for gaining the weight in the first place. Not necessarily so with sin. You can't un-murder someone.
Second, we know that some people can lose weight and keep it off. However, I've never met anyone who was capable of going without sin for the rest of their life.

It works for it's intended purpose. Whether you have a weight problem or a murder problem, you need to address it. Being overweight is only used to represent a deficiency of some kind. It's use as an analogy doesn't apply in all regards.

It is not required that analogized items be analogous in every way.

Have you had your coffee yet?

With regard to sin, their is just one method.

Of course, blood sacrifice.

But with immorality, there are many ways to reform.

The secular approach exists on a continuum as well. There are plenty of people who will tell you you don't need to lose the weight at all - you're fine the way you are. And there are some who will tell you - directly or indirectly - that you're worthless unless you're thin and beautiful.

"The" secular approach? There is no one secular approach.
If you are obese, and people tell you you don't need to lose weight, they are either being polite, they don't care about you, or they are wrong. 
If someone tells you that you're worthless unless you're thin and beautiful they are a shallow asshole (and quite ignorant I might add-- Oscar Peterson was overweight and by some standards unattractive, but his music is a joy to listen to).