Electrolysis is really not an issue with firearms unless your store yours underwater.
In the real world, there in no practical difference between stainless and forged gun parts. Buy the firearm that fits you and you can shoot accurately.
Forged gun parts by definition are stronger, stainless steel parts by definition are more rust resistant. Stainless can be more brittle or can cause galling, but this would depend on the type/hardness of the stainless steel. Since both S&W and SA are experienced gun makers, the strength or longevity of either type of parts is not an issue either.
The S&W M&P has a coated stainless steel, stainless steel reflectance is not an issue. If the stainless was uncoated, a simple bead blasting would reduce the surface finish of stainless to a non-reflective light gray color.
The 2nd Amendment was, and still is intended to protect the individual citizen from Tyranny. Whether that Tyranny originates from
our own Government, common criminals, Progressive Liberalism, or foreign invaders, is irrelevant.