The four major crime types are: Violence, Sex Crimes, Drug Crimes, Theft and Financial crimes.
We treat them very differently when it comes to punishment.
Violence is generally offered relatively low punishments, unless done
repeatedly. Even murder can get you out in as little as 6 years for a
first offense. But repeated crimes of violence often get stacked
Sex crimes committed by men tend to be heavily punished. Sex crimes committed by women tend to be overlooked (Oh, the teacher has sex with a student? Send him to JAIL FOR LIFE. Wait, it was a female teacher? Let her off with a warning. A STERN warning.) Mainly because sex crimes get a bad rap. We think a sex criminal is a violent kidnapping rapist, when they are more likely to be some poor shmuck that got drunk and peed on a school bus. Mainly because the violent kidnapping rapists are so rare as to be newsworthy when they are caught, while people get drunk and pee all the time. It's just bad luck if you get caught and the prosecutor decides to over-punish you.
Everyone knows that drug crimes tend to be punished with huge
penalties. Users get far worse than most think is appropriate, and
don't even talk about dealers. Of course a good lawyer can make it go away.
Theft crimes tend to be punished like Violence - light for first time offenders, heavy for repeat offenders.
Financial Crimes, either get you off with nothing or they throw the book at you.
Why is this?
Most violent crimes are done in a heat of passion and are
unintended. That is most people that hurt or kill someone did not mean
to let it get that bad, but things got out of hand. This knowledge is
built into our legal system.
Well, Drug crimes and Sex crimes are generally considered 'habitual'. That is, if you do it once, people think you are a 'criminal type' that will always do it. As in "he's addicted to drugs, of course he's not going to stop'. People falsely believe the same thing about sex crimes and it also offends our sensibility a lot more. (Despite the fact that sex criminals are less likely to re-commit ANY crime, than other criminals and FAR less likely to to commit another sex crime.)
Theft tends to be planned, but it rarely pays - the amount of money/goods someone can still by theft/mugging/burglary, when divided by the relatively light criminal punishment offered means it becomes a rather poor paying job.
When it comes to financial crimes, lots of people do minor misdeeds. 21% of people think it's OK to cheat on their taxes (Source). Also, many financial criminals work hard at making their activities very complex and hard to understand. Then they claim it was not illegal or, worse case, that they didn't know that it was illegal. What, you mean it isn't legal to create an international charity that owns my office if and pays no taxes if I also live in the office? Sorry, didn't know that.
When you do simple financial crimes - getting caught embezzling money - you go to jail for a VERY long time. Worse than murder, because people know why you did it, and you can't claim it was in the heat of the moment and you regret doing it. But when you do the complex ones, you get away with it.
Worse, we have mandatory minimums that were put into law based on the 'usual circumstances'. This takes away judges discretion, but does it poorly.
So that's why our laws work the way. It has to do with excuses, motivation, reasonableness and difficulty of proving intent.