I hated the helmet law when it went into effect in 1992 (California). After that I wore the smallest helmet I could find, then traded up to a 1/2, then a 3/4, then a full face. Now I wear a modular in all seasons and can't imagine riding without it, although it does sometimes get almost unbearably hot. I feel naked even when I'm moving the across the yard without a helmet.
I wear an Arai full face regardless of temperature, tried the modular, and it didn't work at all for me. For those that choose not to wear, even for a short ride, in my opinion not a smart option. I've ridden half a million miles and never hit anything, then out of the clear blue sky a month ago I hit a car at darn close to 50mph 2 miles from home. My helmet had like a 6" long scrape on it. It was not like a really hard hit to the head, but 6" scrape on the head would have been rather painful, if not fatal. This was not on the GL1800 thankfully.
I have a couple of Scorpion 900 modulars that I like. I use them in the 3/4 configuration with the peak visor unless it gets too cold then I'll add the front. I can't stand driving into the sun with no visor to block it and this helmet also has a retractable internal visor. I don't ride without a helmet.