Yes, lefthanders drag their hand in what they write. When we had esseywriting in school the lefthanders were black on the side of their hand. The text got smeared out on the paper to some extent. And you can not see what you just wrote because the text dissapers under the hand. Righthanders don't have these problems. Since most are righthanders it is best to write from left to right. But leftists should be better off if it was from right to left.
This isn't true of all lefthanders. Many end up crooking their hands around to avoid obscuring the text and smearing the ink, particularly if the teachers who taught them writing were ignorant of how to adapt their lessons for lefthanders. (Mine, for instance, simply told us to "do the same thing in reverse" without demonstrating or going into any detail. Fortunately, I have very good spatial perception, so flipping the images wasn't that difficult for me, but a lot of lefthanders are not so fortunate.)