Allowing my students the choice in whether they play left-handed or right-handed has nothing to do with teaching them good posture, mechanics or technique. My training and experience is to make sure the tiny minority of my students have the choice to play left-handed if they feel more comfortable doing so.
On what basis do beginners decide they'll be more comfortable playing left-handed?
Teachers often make teaching decisions based upon their own experience which includes prejudices and anxieties about how to deal with situations outside their comfort zone.
I'm perfectly comfortable teaching students who are already playing left-handed. I'm also comfortable with saying unambiguously that they enjoy no advantage in doing so.
A lack of an advantage is not a disadvantage.
Nor is it an advantage. Your assertion is hardly a substantive endorsement. We already know that playing left-handed limits one's flexibility in playing other guitars. What advantage offsets this obvious liability?
Left-handed instruments are available across various price ranges, this I know from helping two of my student's parents purchase guitars as presents for Christmas.
No one denies that left-handed guitars are available. But the fact remains that a left-handed player is limited to playing guitars on which the strings are reversed. As a player, I'd find it frustrating that I'll almost certainly never be able to try out a Ambridge, Burghardt, Elliott, Fanton d'Andon, Romanillos, Rubio, Ruck, Tacchi, Velazquez, Wagner, etc. I can watch others play one of these fine guitars, and given a chance to handle one myself, I might plink out a few notes. But to really sit down and play one is very unlikely.
I look at this from a different perspective. I see teaching left-handed players as a challenge and an opportunity.
Teaching a left-handed player is no more challenging than teaching those who play normally. Being a left-handed player, however, is more of a challenge. That some prefer to ignore this issue doesn't make it go away. Nor does it answer the most obvious question about playing left-handed: what's the point? In the absence of any clear advantage, what's the point of playing left-handed? Is it merely to prove that it can be done?
Less obvious in this discussion is the matter of making decisions that lead to wider possibilities rather than fewer ones. A player who regularly decides to do things that restrict his or her horizons will come up against limits that other players don't have to deal with. To me, a good part of a teacher's raison d'être is to advocate decisions that offer more flexibility, not less. A beginner who decides to play left-handed is starting off on the wrong foot. He or she is making a fundamental decision based on either ignorance or the mere desire to be different. Neither is a good way to start. As a teacher, it's my job to help students make good decisions. It's emphatically not my job to shrug and say "whatever."
South Euclid, OH