First of all, recall that ethics aims to provide evaluations of all possible actions. It does this by consistently applying its standards of judgment. In this way, ethics is systematic and objective.
One of the biggest barriers to proper ethical evaluation is when our own attitudes or views distort a fair and even evaluation of things. This is commonly referred to as bias.
If you want to be an ethical person, then you need to make sure you aren’t allowing biases to influence your judgments. Once you do this, you can be consistent in your ethical judgments and not treat some people differently than others due to prejudice.
If you make your ethical judgments suit your own views, beliefs, or interests, then you aren’t really trying to get to truthful ethical judgments. Instead, you’re just trying to make what you would think anyway have the appearance of morality.
One way you might become aware that bias is influencing your judgments is to see if they are consistent in the standards they use.
In the above case you might provide reasons that your family member is an exception to your usual judgment.
But if you use these reasons only when it suits you, then they’re not really ethical reasons. Rather you’re just using them to support your own interest in defending your family member. Likewise, if you refuse to see that other criminals may be in a similar circumstance, then you’re reducing these considerations to keep your bias against criminals.
You can find these kinds of inconsistencies all around you.
Some politicians target certain people they consider to be freeloaders, such as people on welfare. But they then support people that avoid contributing to society, such as companies that are guilty of tax avoidance.
It’s in the interest of many politicians to be inconsistent like this. That’s because big companies have power and people on welfare don’t. To defend their reasoning, they could inflate reasons to support their bias, and minimize reasons that go against it.