There is an awful lot of misunderstanding and assumptions made by right handers about left handers going on here. Let me try and shed some light and give you my perspective as a lefty. Anything that requires each hand to do something different will generally have an orientation preference for leftys & rightys.
Polyal asked "when a beginner picks up a guitar for the first time neither hand as a clue what to do from
the outset so why the ' other way round ' preference ?"
You could ask the same thing about lots of activities that a child or baby learns. They don't know how to do it, nor are they aware they are left or right handed, but they still have a preference. It is how their brain is wired.
When I was young I always wanted to play left handed - it felt natural. I wasn't copying anyone. I think it is to do with the use of a tool and the dominant hand is nearly always used to hold tools. Holding a pick isn't that dissimilar to holding a pen for example. As stated before fretting is alien to both hands. So for me it feels natural to play left-handed because it feels natural to hold the pick with my left hand and using the pick is a more intricate activity for the hand as a whole (as opposed to individual fingers with fretting).
Left handers are not at any advantage playing right handed guitars. That is is something made up by people who aren't left handed due to the mistaken belief that a dominant hand equals finger independence. It doesn't. If this were the case at least some right-handers would play left-handed to take advantage of this benefit and they don't. Left handers play right handed for other reasons: there is a vastly larger selection of right handed guitars, left haded guitars usually cost more, 90% of them are black, tab & notation is in general easier to read, other learning materials are dedicated to right-handers & lefties are often treated as if they should just shut up and become right handed.
Left handed guitars are not a gimmick. Who in their right mind would come up with a gimmick of producing instruments that only have the possibility of appealing to a maximum of 10% of the population (& in reality is less than that due to the number of leftys playing righty)? And who in their right mind would buy them given the aforementioned reasons if there wasn't a fundamental reason for them?
I am genuinely shocked to hear a teacher call left-handers "backward". I understand better than most the reasons for leftys playing righty, but for some kids playing right handed will be much more difficult. Having a greater choice of guitars is no use if you give up because you found it too hard.
