This is a hard question to answer. Sanctions are a way to get nations to behave in our interest which can mean preventing them from acting violently (whether rational or not). I would guess they aren't wholly ineffective either. If nations would act violently should sanctions be impaired and cryptocurrencies impair sanctions, yes cryptocurrencies make violence more likely.

Personally, I prefer sanctions to war but without being more familiar with sanction implementation it is hard to say if they should be ended. Being related to people suffering under sanctions, it's a rather blunt instrument that seems to mostly make citizens suffer and should leaders be unmoved by their people suffering, they probably aren't very effective and instead mostly reduce the power of citizens.