That may depend on what your goals are. To put myself in the IRS' shoes, their goal is to minimize the amount of revenue lost due to fraud. In that view, the important thing to do is to go after the people who are cheating them out of the most money.

If the goal is culture change, that may be different -- but the IRS is probably the wrong entity to address it.

I will say that I have not noticed that lower-income people have any greater sense of "cheating is OK" than higher-income people. My observations are not necessarily representative of the wider culture, but it looks to me like the percentage of people who think cheating is OK doesn't change based on income.