To add on to the answers by Rachel and RhysW which I agree with.
Don't Throw the Baby Out with the Bathwater
Rather than focusing on the intent of the person asking the question, I think the emphasis should be on evaluating the potential for the question to help well-meaning people in the future.
Specifically in regards to this question, regardless of the asker's intent, I think that there are many circumstances in which the answer to this question could help people in the future. For instance:
John has an accountant do his taxes. He is currently undergoing a background check for new employment and just received a letter from the IRS stating he will be audited. Will that show up on a background check?
Jane has been living in France working for a French multi-national for the past three years. Due to the Foreign Earned Income Exclusion she was told she didn't have to pay taxes in the US and did not file a return. After returning to the US she hired an accountant to handle taxation when she worked in both countries during the year. She is currently undergoing a background check when her accountant lets her know she still had to file a return even if her tax liability was zero for the year. Will this show up on a background check?
Both of these situations are well-meaning people who end up with the same result (a period where they were not filing taxes properly not due to ill-intent). Suggesting that we should remove a potential resource from John and Jane because we assume that Alexander wants to get around paying his doesn't seem like the best approach to make if we truly want to be a resource in the future.
Legality and Ethics are not Absolute
Would this question be appropriate for the site?
I am a 19 year-old intern in Buffalo, NY. My coworkers invited me to go drinking with them in Toronto for my farewell party since I can't drink legally in the US. Is this a good idea?
What about this one?
I am an unmarried Englishman who does business in Singapore. When visiting important clients on a business trip, they insisted I visit a brothel with them. It was made clear that if I do not, I will lose the project and likely my job. While I have no moral objections, what potential consequences will it have with my company if they find out?
Or how about this one?
It is 1965, I live in Illinois and am interviewing for a job across the border in Missouri. Interracial marriage is illegal in Missouri but legal in my state. Is it ethical to lie to my employer about the race of my spouse if asked?
Ethics/legality are rarely clear cut. Laws change over time, and by country, as do ethical codes. Rather than judging which questions are appropriate or not based on our own assumptions, we should focus on getting at the heart of the question (how to tackle ethical quandaries) which can definitely help future visitors. While these may seem like extreme examples, I think they are just as valid in tackling workplace issues as questions like, "Should I go to an interview I don't intend to accept the job (if offered)?"