"I generally don't mind lane splitters, but I'd prefer it if they'd use the shoulder (if there is one)."
In California, the only state where lane splitting is legal, to the best of my knowledge, riding/driving on the shoulder is not legal. Elsewhere you're breaking the law either way, and I tend to agree that the shoulder might be safer.
California's law was intended for air-cooled bikes, which were predominate in my formative years. 100 degrees and above was normal and expected in the Sacramento Valley near where I grew up during the summertime.
I don't have an opinion as to whether that law needs to be revisited to account for water-cooled bikes, but I tend to want to leave well enough alone.
Bikers splitting lanes makes me envious, not angry.