That is just strategy. Lefty's don't need to bunt, just go the other way or up the middle. Be a complete hitter. If teams aren't going to be able to take advantage of hitters weaknesses then they shouldn't be able to throw certain pitches or pitch to locations that hitters can't handle either. Shifting the defense against lefty's is, as Mr. Burn's would say, playing the percentages. If teams can't play percentages then there should be no pinch hitters, no changing pitchers to get a favorable matchup, no starting a bench RHB over a LHB against a tough lefty.