I wouldn't call it unethical per se'. It's less sustainable than white hat SEO for sure. When people rank sites using white hat techniques, they're thinking about the long term. They could be ranking the site to make it some money and then sell it as an asset later on. They could be a legitimate business looking for long term leads. It could be anything in that sense.
Black hat SEO, on the other hand is more for quick cash. It's churn and burn in a sense. You're trying to rank for something that you know can make you money but it's not going to last you more than a couple of weeks, or months if you're lucky.
In my honest opinion, Google shouldn't really be a business that you should be following 100%. I see people following all of Google's terms and conditions and making sure that they don't get on the wrong side of them in case they get a penalty.
Google doesn't care about you. If you're not making them money, you're of no concern to them. It's the main corportations out there that Google cares about. These guys dish out thousands of dollars every day on Google which provides their bulk of revenue. People like you and me though, we aren't seen as special in their eyes.
Think about it, Google could kill your business overnight. You could be doing white hat SEO for a couple of months and see rankings, but once the update hits, your $100 a day business is now earning $5 - $10 per day if you're lucky.
That's why I prefer the black hat route. You're playing by your own rules and making money as quickly as you can.
The best way to utilize black hat SEO is to rank for an affiliate product that gives recurring monthly revenue. If you rank for 7 days for an affiliate product that costs $47 per month and you managed to get 200 people to buy the product in that time frame, you're looking at just under $10k a month from a simple black hat SEO ranking technique.
Hope that helps.