Capturing Pinned Knight with Unchallenged Bishop

I have recently been doing a bit of homework on general opening theory.  As usual, there seems to be a certain amount of contradiction, even in the same books!

One thing that seems to be an opening standard is NOT to capture a pinned knight with the bishop pinning it until the bishop is challenged (i.e. 'putting the question to the bishop'). The reason given is that it saves your opponent a tempo. This makes perfect sense.

What has now become apparent to me is a further reason not to capture - i.e. the advantage of the bishop pair.  The argument goes that the side with the bishops can open the game to their advantage.  This is especially true when white has the bishop pair.

To illlustrate this point, I saw a game which was Lasker - Blackburne. Blackburne played Bg4, pinning white's Nf3.  Then he captured Bxf3 without having h3 played.  Next white move was gxf3 (!) with the following comment (remember that the N was pinned against the white Q):

''Black's lack of a white squared bishop means that he can hardly take control of the weak white squares on the kingside. The queen is needed on the queenside. And besides that, gxf3 opens the g-file to attack the black kingside and brings a pawn to the centre.''

All very good.  It would seem that Bxf3 was a dreadful mistake and Lasker then exploited his advantage magnificently to prove the point. Great.

Now comes the problem. The author then gives an example game of how to play against the two bishops, with Chigorin as black.

Chigorin played Bg4 pinning the Nf3 (you can guess what is coming next) and after Bxf3 without h3 we get the comment  ''Chigorin was a known advocate of the Knight and Bxf3 is an integral part of the Chigorin defence''. So now Bxf3 is good??  To compound everything, Chigorin then goes on to play Bxc3 later (that is kings Bishop takes White Queen Knight) again unchallenged and goes on to win the game.

And who was white in this game? You guessed it -  Lasker. And it gets better, this game was played seven years after the first one.

 It seems to me that this kind of contradiction is rife in chess literature.  I know there are always (nearly always) exceptions to the rule, but what I am talking about here is a few moves into d4 openings, not a complicated middlegame.  I would appreciate comments, especially from stronger players who know about general opening theory.  Thanks in advance. Mxd