Word for when something wrong is made to seem normal because it is common?

From your own moral point of view, you could say that she has a skewed moral compass and that she's simply rubber-stamping the mores of the morally bankrupt society that we live in.

Or something like that ...

You might be looking for a term such as ethical drift.

Here is an example from nursing ("a gradual erosion of ethical behavior that occurs in individuals below their level of awareness"), and here is one from business ("Slowly drifting away from professional and legal standards and personal standards a business person has long been associated with"). Have a look and see what you think.

The action (of asking such a question) might be referred to as gauche (“Awkward or lacking in social graces; bumbling”) or tactless (“having no tact; unaware or intentionally inconsiderate of someone else's feelings”). The behavior of asking might be considered déclassé, except that dictionary-usage of déclassé is along the lines of referring to a person “degraded from one's social class”, I think, rather than one engaging in degrading behavior.

This might be minimization or reduction, the opposite of exaggeration: downplaying, discounting, or understatement. The purpose is to make an unethical act seem more trivial than it is:

Minimizing makes unethical transgressions seem smaller. The person who admits that he or she did something wrong but states, "It's not that big of a deal." Minimizing is one of the most common ways we reduce our feelings of guilt and worthlessness resulting from transgressions. --The Ethical Executive

EDITED TO ADD: In your example: When asking "would you cheat?" so matter-of-factly, as if it were a common thing to ask or a reasonable option, the questioner might be minimizing the negativeness of cheating.