Grammatical corruption

Its, it's and 'tis! My colleague Tony castigates me repeatedly for the use of "it's" for the possessive pronoun. In an editing workshop last week I posed a question to the group,by asking why, if a mule's ears are long and hairy,why not "it's" ears are long and hairy? To say that the possessive "its" ought not have an apostrophe, while the noun it reflects does, makes no sense to me. The consensus at the workshop was that it differentiated the use of the two words. Why would anyone care to go there? The context declares it! Then I read in the grammar detective, that "it's" as a possessive pronoun, was used on a regular basis a couple of centuries ago but was changed to "its" when "'tis" became deemed archaic, so "it's" was substituted for "'tis" as a contraction of "it is" and "it's" was shoved out of the rightful place as a possessive by the grammarians. What the hell! I can hardly wait to confront Tony, start using "'tis" again, for "it is" and talk about mule's ears without a lame excuse about differentiation. What a contrarian either I am or English is!