I like Google's mission statement -- Don't be evil. It's probably an anagram of something, but I still like it. If you have to lie, cheat, steal, defraud, lose sleep, hide, dodge the law in any way, break the rules, or generally behave badly to make your money, then don't do it. It isn't worth it.
If earning money or being wealthy stops being fun -- and by being bad, it really will stop being fun -- then there's no point doing it. If you don't enjoy the challenge of earning money in a decent way, it's best to go and do something different.
I knew a major criminal once. He told me it was no fun being "crooked" because, in fact, he had to be a lot more law-abiding than the rest of us. He couldn't risk getting pulled over by the police for speeding or any minor motoring offence; no late-night parties in case the police got called out; no flashy car to draw attention to himself; and no lavish lifestyle in case it put him in the spotlight.
But there is more to living a clean life than being able to speed or have parties. Living a life where you make your money from being good lets you sleep nights. You get to look your kids in the eye -- and yourself in the mirror -- with the added bonus of a feel-good factor. No amount of money can buy that.
If you have to resort to being wicked, it means you've failed; you've lost the plot. It means you haven't been able to do it properly. It means you're scraping the barrel. It means you haven't been able to think of a proper idea. It means you've been lazy, desperate, noncreative, and boring.