I know that its mostly preference, but my reasons:
1. with a turbocharger you have more choices
This depends on the car mostly, but for the case of the Mazda3 this is correct.
2. you can make more power out of a turbo
Incorrect. Having a turbo doesn't by default make more power than having a supercharger. Just as the supporting pieces make a difference along with the different trim levels of turbos, the same rules apply to superchargers. Superchargers have come a long way recently.
HKS agrees.
Removing the exhaust manifold, replumbing oil lines, routing intercooler pipes, etc. is a lot easier? Interesting theory you have there.
That is, if you are running a intercooled supercharger its about the same amount of work.
350z supercharger kit by HKS.
RSX turbo kit by HKS. (The 350z supercharger comes with an oil cooler too, don't be fooled.)
4. easier to upgrade if you wanted a different brand/ type
Yes and no. Going from a T25 to a T3 (for example) requires a new manifold, exhaust, plumbing, etc. Not sure what you were going for here.
5. instead of using power to make power, it uses exhaust gases to spool up the turbo so its free creation of more power.
Nothing is free, 99% of turbo manifolds would make an awful N/A header, and drawing the pre-turbo-spooled air through all that extra plumbing isn't exactly leaving you with 100% stock factory power either.
Wow, pulling that one out of the air I see.
I would agree with you here, but only if you can explain why.
People to stop posting dumb s*** like "why woudl you want a supercharger when turbos are better anyway" as a start.