Imagine the following scenario:
Your thriving web business has grown into a huge success, and you have very high positions for most of your targets and are #1 in Google for a search of "widgets." You're continuously building content, and taking steps to stay within Google's guidelines, using only sanctioned techniques, and life is good.
But one day you discover that "widgets" is #3. So you redouble your efforts and make every effort to optimize what you have. But your ranks slide further, along with traffic and conversions. The enterprise quickly becomes more difficult to manage, as the lack of traffic begins to harm the infrastructure.
So you hire an SEO professional who looks at your site and tells you the reason you're no longer on page 1 has something to do with those 5 websites ahead of you that are using black hat to garner rank.
The first ethical question is, "Are you willing to report those sites to Google that you know are outside the guidelines?" (If you answer, "no" to that question, sell your business and join the monastery.)
However distasteful you find it, your employees and their families require that you report these sites and try to get back to page 1. So you do it. But a week later, nothing has changed. You're still on page 2, with no traffic. So you report them again, and again. But the sites remain ahead of you, benefiting from their non-sanctioned techniques. You're getting desperate.
Then your SEO tells you that he knows how to get you back on page 1. Because when you compare your content sets with those of the sites ahead of you, he shows you that your site is far more relevant from a content point of view. He says that if you only did the same non-sanctioned technique as those above you, you would actually rise ahead of them because of your amazingly relevant content sets.
The second ethical question then is, "Are you willing to use black hat techniques if Google is unwilling or unable to enforce their standards effectively?"
Before you immediately reject this line of thinking, first remember what 'black hat' means - it means using strategies that are unsanctioned by Google. But these strategies are not ILLEGAL, or even UNETHICAL, they're just outside the guidelines. And given that link buys are now considered black hat, and that most sites in competitive fields are competing with sites that buy links, what's the real issue here? Do you want to sit outside the search because you want to remain compliant? How stupid is that?
So you can see that the issues are much bigger, and much more unclear than simple black hat, white hat considerations. Sometimes the preservation of the enterprise requires you to think outside the box. Of course you don't want to put the business at risk, but if you follow the above analogy, your business is already at risk, in fact it's being harmed by NOT taking those risks.
Blind allegiance to failed rules is stupidity.