I'm trying to find either a word or a phrase that describes a person who who is blind to the negative consequences of their actions even though the consequences should be obvious to them.
not aware of or not noticing something, esp. what is happening around you:
She was often oblivious to the potential consequences of her actions.
Someone that is blind to the consequences of their actions is "Ignorant", though the contextual clues suggest that a better word to use might be "Naive" as it refers to one that is specifically unaware of the "consequences" of their actions rather than lacking a general "understanding" of their actions. Naive also entails that the person is "blind" to consequences (in a negative sense) of their actions and so can only see the "positive" outcome of what they do.
Some synonyms of the word ignorant are as follows (quoted from Oxford Thesaurus of English).
without knowledge, unaware, unconscious, insensible; unfamiliar with, unacquainted with, unconversant with, inexperienced in, uninitiated in, blind to, oblivious to, naive about, innocent about, green about, a stranger to; uninformed about, unenlightened about, unschooled in; informal in the dark about, clueless about, not knowing the first thing about, not having the faintest about; literary nescient, strange to "I was largely ignorant of the effects of radiotherapy"