I agree that high-precision protractors and ultra precise alignment makes for sense for a dealer than a home alignment. The big problem is that no matter how precise the alignment, built-in errors in the manufacturing of styli, cantilevers, and cartridge suspensions pretty much dwarf minor errors in user alignment of the cartridge. Look up zenith error. Even with extremely expensive cartridges, zenith error can be very high because it is really hard for the manufacturer to spot the error when mounting the stylus. The kind of microscope required to see and measure zenith error cost as much as a decent automobile. Unless you have a conical stylus, zenith error will put the wrong part of the stylus in contact with the groove wall which would mean more wear on both the record and the stylus. An analysis of zenith costs big money, but, it will allow one to justify seeking correction for gross error from the manufacturer or making compensatory adjustments for more minor error (correction would involve twisting the cartridge away from perfect alignment of the cantilever with the line on the protractor).
Some of the other alignment measurements people take also don't make that much sense, such as insisting on a 92 degree stylus rake angle. This is only roughly the correct angle under dynamic (while record is in play) conditions. If you make a static measurement using a USB microscope, you will not be setting the angle to what it will be while the record is playing. Again, there are complicated ways of measuring the angle under dynamic conditions, but, one is really better off just setting an approximate angle (tonearm perfectly parallel to the record surface) and then listening for improvement in the sound from trial an error deviation from the approximately correct position.
