To understand how mob psychology can make common wisdom of complete nonsense consider these claims by Voros McCracken in 2001:
"There is little if any difference among major-league pitchers in their ability to prevent hits on balls hit in the field of play."
"The critical thing to understand is that major-league pitchers don't appear to have the ability to prevent hits on balls in play."
In support of that claim, McCracken goes on to site the following about pitchers' Batting Average on Balls In Play ( (H-HR)/(BFP-HR-BB-SO-HB) ):
"The vast majority of pitchers who have pitched significant innings have career rates between .280 and .290."
Of course McCracken's claim caused a sensation in the statistical community. It greatly simplified the troublesome need to consider team defense when evaluating pitching (FIPS anyone?) It all but eliminated the need to consider pitching when evaluating fielding. As a result, the statistical community developed all sorts of new statistics working from his premise and it has been extended to hitters.
Now you would expect some healthy skepticism of that claim. The obvious question is what was the league BABIP in 2000 when McCracken did his "study?" If the vast majority of successful pitchers, those that got a significant number of outs, are all above average in getting hitters out on balls in play you would probably conclude it is unlikely they have no control over it. But the league BABIP was and is around.300. That is 10-20 points higher than the figure sited for the "vast majority" of successful starting pitchers as identified by McCracken.
Now you might think this was overlooked all these years. It wasn't. That .300 average is sited on the Baseball Prospectus site as the "typical" BABIP for pitchers. In fact, that claim is itself inaccurate. The average (mean) for all pitchers is .300, but the typical (median) pitcher's BABIP is actually considerably higher since the best pitchers face more batters than those with higher BABIP. But either way, the best pitchers have the best BABIP, well above an average pitcher.
As others looked at the numbers and raised troublesome question about McCracken's basic premise finding numerous examples that contradicted it, they were explained as "outliers", ground ball pitchers, etc..Many pitchers had career BABIP far lower than the .280 McCracken claimed and the range of career. BABIP for pitchers goes from as low as .250 up to .350. Very similar to the range in hitter's batting averages. Combined with McCracken's own data showing the vast majority of successful starting pitchers have above average BABIP, you would think pitchers influence over whether a ball goes for a hit had been proven. Successful pitchers are successful, in part, because they get hitters to put the ball in play in ways that make it easy for their fielders to turn them into outs. That certainly is traditional baseball wisdom. And the actual numbers support it.
Nonetheless, McCracken's basic conclusion has become an urban legend. Like any urban legend, once believed, no amount of facts will cause people to abandon their belief in it. None of us like to admit we were enthusiastically wrong.