It is advantageous for a society to have a means by which all can be cleansed. If people do not have such an opportunity, they might have a greater probability of becoming repeat offenders.
This parshah is a sin offering, a burnt offering, a meal offering, and an offering because one has a "lesion of tzara'th." Is the kohen attempting to cover all the bases just in case the poor person has done more than have a lesion on his skin? Or is the lesion simply a pointer that the individual has messed up in a big way?
Funny that this offering is for a male. Don't women have lesions as well?
“And he shall slaughter the guilt offering lamb, and the kohen shall take some of the blood of the guilt offering's and place it on the cartilage of the right ear of the person being cleansed, on the thumb of his right hand, and on the big toe of his right foot.”