An American military presence is eastern Syria is surely a risk. But the idea that there are no rewards is nonsense.
While I wouldn't send 150,000 ground troops to Syria (and never have been interested in that), the idea that a small commitment in support of friendly forces on the ground isn't in America's interest is just not true.
Securing Iraq is surely an important American interest. A hostile Iraq is a problem for us and our allies. And three wars and a long quasi-war under five presidents shows that. Bush 41 waged the Persian Gulf War and enforced a no-fly zone; President Clinton enforced a no-fly zone and struck Iraq's WMD infrastructure in the Desert Fox air campaign; President Bush 43 waged the Iraq War; President Obama returned to Iraq to begin Iraq War 2.0; and President Trump continued Iraq War 2.0.
So protecting eastern Syria is in America's interest to protect Iraq. Eastern Syria was a haven for Baathists after the overthrow of Saddam, a "rat line" for al Qaeda terrorists during the Iraq War, and the launching pad for ISIL to take over western and northern Iraq in 2014.
Demonstrating that America will stand by those who stand with us is important. Are we really to abandon the Kurds and Arabs who fought and died to fight ISIL? How will we get help in the future and avoid sending 150,000 troops to carry out a mission somewhere else if America is not trusted?
Blocking Iran's overland access to Lebanon and undermining Iranian efforts to turn Syria into a satellite are important. Or do you still believe that the 2015 Iran nuclear deal will turn Iran into a responsible non-nuclear regional power?
A free region within Syria as an alternative to refugees who might otherwise flow to Europe, Lebanon, or Jordan where they cause problems for our allies and otherwise promote instability is useful. Note that one reason Turkey is carving out areas in northwest Syria is to be an alternative (to Turkey) refugee haven.
A role in protecting Syrian Kurds will give America some leverage to reduce the threat to Turkey from Syrian Kurds backing Turkish Kurds. That might help ease American disagreements with Erdogan's Turkey until pro-American Turks can regain strength within Turkey.
Denying Russia an easy win in Syria is in America's interests both in itself and to keep poor Russia from being able to pivot back to Ukraine to complete their war in the Donbas and potentially move on to other targets to restore the Russian empire in the west.
And having the ability to pressure Assad either diplomatically as we now seem to intend or by shielding an eventual non-jihadi Syrian force capable of being the alternative to Assad's rule would get revenge on the Assad family regime for their role in a lot of American dead troops from Lebanon to Iraq.
Are these things really of no benefit to America and worth the effort of a relatively small commitment on the ground east of the Euphrates River line (the Deconfliction Line, or DCL, as I call it) backed by air power?
And if we don't make this commitment, what problems will arise elsewhere as a result that would require the commitment of 150,000 American troops on the ground?