The West wants oil security for obvious economic reasons and generally likes to see/promote power balances across the globe, so unfortunately the West’s foreign policy dictates, in the pursuit of that ‘balance’, that it isn’t too important if a country has a bastard of a dictator, as long as he is OUR bastard of a dictator.
In the Middle East decades ago under the Shah of Iran, Iran was a friend of the U.S,, once the fundamentalist Ayatollahs took over Iran, Iraq (with Israel and later Egypt) was our counterbalance to Iran and Syria.
Of course in Middle East politics, Shia versus Sunni is the main ‘political’ line.
In current Iraq, the democratically Shia President (whatever) has ignored the wellbeing of the Sunni and Kurds and snuggled up a bit too much to Shia Iran - so the domestic Sunni’s and Kurds already wary of their own Shia government - now have Iranian Shiites in as guests of their government, invited in to kill (Jihadi) Sunni’s.
So now the Iraqi Sunni’s (and Kurds) have to be concerned about Iraqi, and worse Iranian Shiites, declaring ‘open season’ on EVERY Sunni within Iraq they find, in the legitimate aim to purge Iraq of ISIS.
Somewhere, Iraq has just under 300,000 soldiers, to fight the ISIS hard nuts numbering no more than 10 to 20,000, but it seems beyond them to sort out an Iraqi force of Shiite soldiers, that will not sympathise with the disenfranchisement of Iraqi Sunni’s by their own government by deserting their posts, and fight for their own country.