True, you're not wrong about the idiocy of '3 strikes' laws, but the problem with them is specifically that they remove discretion from the court, rather than the general concept of escalating punishment for serial offenses. If someone steals a pair of socks, a head of lettuce, and a blanket, they should not be automatically treated the same as someone who steals a Chevrolet, a Lexus, and a Porsche.
Sentencing laws in general are a really terrible idea IMHO.
Sentencing guidelines do serve a legitimate purpose, though. The problem with giving judges very wide discretion is the sentence you get doesn't depend so much on whether you were the socks vs Chevy guy as much as to which judge your case was assigned. If car thief A gets three months and car thief B gets three years for exactly the same crime that's fundamentally unfair.
Sentencing laws in general are a really terrible idea IMHO.