Why choose a manual when car was not designed for it?
I don't want to get into a debate over which tranny is "better" in terms of fun, feel etc etc but rather let me give you an example of how the M division really approached this last generation of M cars starting with the e60 m5 and m6 prior generation with the s85 v10 revving to 8250. They did not even offer the car nor test the car with a manual gearbox. That says A LOT from a compny who actually still puts manuals in virtually all of their regular series cars. If anyone has seen interviews with the M people over this, the engine simply was a terrible fit for a manual box in terms of maximizing its performance and enjoyability.
The 7 speed SMG or now DCT was used because it allowed a much closer ratio tranny that allowed the engine to stay in its quite narrow power band in the high revs as we all know at revs below 5500 there is not much to write home about. They finally stuck a manual on just for the US because we complained but in the end it was a horrible fit in terms of form vs function of the intended purpose of the car.
The new M5 is actually a car that goes well with a manual and a DCt is not nearly as beneficial from the aspect of needing to keep the engine in its limited power band since the powerband is much broader.
So back to the m3, if you have a top engineering company like M, designs a 8400 rpm v8 designed to operate above 6k rpms for extracting power, why would you not want to choose the transmission that it was designed with and designed to enable you to stay in that power band since that is where the power is.
A manual means you cannot stay in the powerband as easily and with slightly larger gaps between gears, especially after 3rd, you are dropping well out of the power band compared to the dct which means you are using hundreds of RPMs to simply catch back up to get into the powerband where as the DCt will shift and keep you right in the band.
I understand the history and the "feeling" but if you choose a car designed with a certain tranny and technology-why not embrace the technology of this car or otherwise choose a different car that was designed with a manual tranny in mind-even the new m5 or a mustang or a regular 335i n54 motor etc.