Shouldn't sentencing guidelines be abolished?

Because of sentencing guidelines, criminals get their punishments reduced. If it suits the judge's taste, they get leniency; if not, they get severe punishment. And if it's their own business, they get even harsher penalties. Isn't this destroying the country?
In an article today, a teenage girl who habitually harassed peers by burning them with cigarettes and distributing nude photos was given a suspended sentence on the grounds that she is a minor and can be rehabilitated.
Can that kind of personality truly be rehabilitated? Won't people just think, "She did all that and didn't even go to jail?"
Wouldn't the right direction be to ensure they receive proper punishment so they truly repent for their wrongs?
The law should strictly impose severe punishment, and sentencing guidelines should be abolished entirely. While changes may occur to keep up with the times, I believe the law should be applied mechanically, as prescribed, and without discrimination against anyone.
Law-abiding citizens have nothing to worry about even if punishments become stricter, because they have nothing to be punished for.