I consider myself to be very left-hand oriented. I write, use my mouse/trackpad/trackball in my left, play a left-handed guitar, and golf lefty. I'm a switch-hitter in baseball, but prefer my left, and throw lefty. My shotgun is bottom-eject, because I shoot lefty, too.
Right-handed tools are the bane of my existence. I hire contractors to do all my home repairs/upgrades that involves power tools. I won't risk it. As a computer-oriented professional, my hands are too important to lose them, or any of my fingers, in an accident.
The problem with mice isn't that left-handed mice aren't available, it is that schools and businesses will blindly purchase right-handed mice. Even worse, none of the operating systems make it quick and easy to change the mousing preferences. This should be a clear and visible option on the login screen, but it isn't. In all Linux distributions, in MacOS, and Windows (through to at least 7), you can't switch your mouse binding without digging into relatively obscure options, that can only be accessed through use of the right-handed mouse, or relatively arcane keyboard-oriented knowledge. That is assuming the school/business hasn't wired the mouse in a way where it is difficult or impossible to use it on the other side of the keyboard. The average user will default to learning how to use the mouse right-handed before they figure out the mouse can be used left-handed, or spend the time to configure every public access-terminal.
The anarchist in me has left public computers configured for left-handed use after using it, for the sake of the next left-handed person, and for the education of the right-handers. If they can discriminate...
In the USA, businesses and schools are not required to provide left-handed computing facilities or otherwise assist left-handed employees, contractors, or students. The ADA does not protect left-handedness as it is a physical characteristic, and not an impairment. However, culturally, left-handed people ARE impaired and would benefit from government mandated accessibility in schools and businesses.