Of all the belligerents in the current middle east conflict, the Kurds are the easiest to sympathize with and understand.
Their political parties are usually the most progressive of the region, sometimes dramatically more progressive.

So what's the harm in backing them? Simple put, all of the neighboring countries distrust the Kurds.

For instance, it's well known that the two biggest enemies of ISIS are the Kurds and Iran.
What isn't so well known is the PJAK Party of Free Life of Kurdistan. They are a Kurdish liberation group based in Iran, listed as a terrorist group by the United States in 2009, and loosely affiliated with the PKK. Half of the members are women.
They were founded shortly after our invasion of Iraq, and the United States allowed them to operate from Iraq for years.
Less than a month ago the PJAK attacked a military guard post, killing 20 people.
This past week, the Iranian government responded by attacking a PJAK position and executing Kurdish political activists.

Many Kurds in Iran complain of oppression of their cultural identity and of discrimination, mainly for government jobs, and want a regional government like that of the Kurds in Iraq...
Iran's seven million Kurds make up around 10 percent of the population. Most live in Kurdistan, a region in the northwest on the border with Iraq. It is among the most politically active regions in Iran, where little dissent is tolerated. In recent months, workers and activists have held a series of demonstrations and strike actions calling for equal rights...
"Iran wants to make it clear that nuclear deal should not create any new expectation among the Kurds to seek more freedom," Hemn Seyedi, a political analyst based in London, said.

Iran has also grown wary as Kurds around the region have made significant political and territorial gains, as well as some powerful new friends.

In Iraq and Syria, Kurdish fighters have become key allies to a U.S.-led coalition fighting Islamic State, taking on the ground offensive while the fighter jets back them up from the air.

Washington considers the PKK a terrorist group, but cooperates with related entities such as the Democratic Union Party (PYD) in the Syria and Kurdish peshmerga forces in Iraq.

However, Turkey last month began a campaign of air strikes against the PKK after the militants stepped up attacks, saying Turkey had violated a ceasefire agreement.

"Iran is also worried about the movement of PKK fighters near its Iraqi border. PKK fighters might come to Iran to escape recent Turkish bombardment. That's why Iran is showing a stronger fist to Kurds in recent months," said analyst Seyedi.