Our Gemara quotes a Mishna that skins that are worked and processed lose their status of Tum’ah, with the exception of human skin which remains impure.  Based on this difference, there is an important polemic between a Saducee and a Sage recorded in Mishna Yadayim 4:6. 

The dispute is as follows: How does rabbinic law make sense? They render scrolls of scripture as impure, while Greek sacred literature (possibly referring to Homer) is pure? They render the bones of even Yochanan the High Priest impure but not the bones of donkey.

אוֹמְרִים צְדוֹקִים, קוֹבְלִין אָנוּ עֲלֵיכֶם, פְּרוּשִׁים, שֶׁאַתֶּם אוֹמְרִים, כִּתְבֵי הַקֹּדֶשׁ מְטַמְּאִין אֶת הַיָּדַיִם, וְסִפְרֵי הוֹמֵרִיס אֵינוֹ מְטַמֵּא אֶת הַיָּדַיִם. אָמַר רַבָּן יוֹחָנָן בֶּן זַכַּאי, וְכִי אֵין לָנוּ עַל הַפְּרוּשִׁים אֶלָּא זוֹ בִלְבָד. הֲרֵי הֵם אוֹמְרִים, עַצְמוֹת חֲמוֹר טְהוֹרִים וְעַצְמוֹת יוֹחָנָן כֹּהֵן גָּדוֹל טְמֵאִים. אָמְרוּ לוֹ, לְפִי חִבָּתָן הִיא טֻמְאָתָן, שֶׁלֹּא יַעֲשֶׂה אָדָם עַצְמוֹת אָבִיו וְאִמּוֹ תַּרְוָדוֹת. אָמַר לָהֶם, אַף כִּתְבֵי הַקֹּדֶשׁ לְפִי חִבָּתָן הִיא טֻמְאָתָן, וְסִפְרֵי הוֹמֵרִיס, שֶׁאֵינָן חֲבִיבִין, אֵינָן מְטַמְּאִין אֶת הַיָּדָיִם:

The Sadducees say: we complain against you, Pharisees, because you say that the Holy Scriptures defile the hands, but the books of Homer do not defile the hands. Rabban Yohanan ben Zakkai said: Have we nothing against the Pharisees but this? Behold they say that the bones of a donkey are clean, yet the bones of Yohanan the high priest are unclean. They said to him: according to the affection for them, so is their impurity, so that nobody should make spoons out of the bones of his father or mother. He said to them: so also are the Holy Scriptures according to the affection for them, so is their uncleanness. The books of Homer which are not precious do not defile the hands.

While, as noted by the commentaries, the actual reasons are different than those stated in the Mishna for polemical purposes, it does offer a valuable insight.  That being that one must be on a certain level of purity to be susceptible to an impurity.  Similar to the idea that a white garment shows more stains than a black garment.  This can explain why certain environments, communities, yeshivos and schools can simultaneously make some people less religious, and paradoxically, others more religious.  How often has non-Orthodox “kiruv” ended up bringing people to Orthodoxy, while on the other hand, those same sources may make others less Orthodox.  Furthermore, we have all heard of those who go through a pro-forma conversion for the sake of marriage and then end up becoming more religious than their spouse!  One is on the way in, and the other is on the way out!

It is important for us to keep in mind that similar processes can have radically different effects based on where the person is holding.