Philosophers call that a moral hazard. That is, it creates conditions under which your actions with a narrow definition of interest led further down to unintended consequences that actually harm both your own interests and others'. As I said in my opening remarks, once you start carving out exemptions for domestic political reasons, everyone else starts asking the same, and therefore you create a Swiss cheese of sanctions. Everyone starts jumping from one part to another. It thus undermines the sanctions.
Sanctions work in the long term when they are united and they are consistently applied. You're not going to be accused of hypocrisy when you're asking other countries in, say, the global south to sanction or to join the sanctions against Russia at the same time that you're providing carve-outs for your domestic political or economic interests.
So it significantly undermines credibility as well as the sanctions regime.