A stiff suspension does not necessarily make for a good handling car. A perfect example of this is earlier years of the 335i with sport suspension and RFTs. The suspension was not capable of keeping the tires in contact with the road surface and the tires bounced all over the place on rough surfaces. This IMO did not make for a good handling car and was certainly not confidence building.
There is a "sweet spot" or more accurately a "sweet range" for suspension stiffness and too stiff can be as detremental to handling as too soft.
The idea of a "race car for the street" does not really work as streets are very different (i.e. bumpier) than race tracks. Even on a race track you reach a point where as the suspension get stiffer performance begins to suffer. So although it may feel more like you are driving a race car when you have a very stiff suspension whether there is actually a performance advantage is another matter.
FWIW the driving coach at the Lime Rock Club, who drives an M3 around the track as part of his job and probably does a few thousand laps per year, told me that the M3s are fastest around the track with 18s and the suspension on the second hardest setting.
As for the argument that 19s look better, that is a matter of personal taste, but IMO you are either going for performance or style. If you are willing to give up performance in the name of style that is fine but don't confuse your priorities.
Drivers Club at Lime Rock - International Motorsports Research Center
Madison Avenue Sports Car Driving and Chowder Society (Only a Vice President)
Polish Racing Drivers of America (PRDA)
The Glen Club - Sports Car Club of America