I think the X2 is has the highest fare evasion period and that's only 50%.

Also not for nothing, DC public school students get free metro rides, so a lot of "fare evaders" were riding free anyways.

Also of note, free fares for busses greatly speeds up the bus (no waiting for people fussing with dollars). Plus, I remember the Kansas City DOT director commenting that something like 75% of incidents on busses where the police are called related to fares. So you speed up the busses, avoid conflicts, drivers are safer, police can focus on more important issues

Oh and most fare boxes only cover something like 10-30% of costs anyways, so you're not sacrificing a lot for large improvements. And it helps the poorest people access the city.

Lastly, our highways are heavily subsidized and free to use, why not the bus?