Why Does Catcher's Interference Count Against OBP?

Catcher's interference occurs when a batter hits the catcher's mitt during a swing, allowing him to go to first base. The rule was introduced in the 19th century after batters complained that Connie Mack would mess up their swings by swatting the bat with his glove. 

    If a batter reaches by catcher's interference, it is counted as reaching on an error, counting against his OBP. While I understand the mentality of calling it an error, I don't agree with punishing the hitter in any way. As in the case of a hit by pitch, the whole point is that the batter didn't get a chance to hit, and is awarded a free pass as a result. Unlike a hit by pitch, which raises a player's on base percentage, catcher's interference actually lowers it, even though the batter reached base (and certainly didn't fail to do so through any fault of his own). 

    This all raises another interesting question: when evaluating defensive players, what should be scored as errors? As it is, fielding errors, throwing errors, and catcher's interference all lower fielding percentage, but other mistakes such as wild pitches, passed balls, and balks (not to mention walks and hit batsmen) do not, but are isolated. I personally would like to see catcher's interference isolated, and continued to be scored as errors, but I see no need for them to do anything to a batter's OBP since neither he nor the pitcher won their battle. While one can argue that there is value in wearing an incoming pitch instead of getting out of the way, nobody would argue the same about catcher's interference. I'd probably also like to see wild pitches, passed balls, and balks scored as errors because the defensive team gave away free bases through its own fault. What do you think?