Is the author biased, and if so, in what way?

If you're writing a book about a contentious issue like housing, it's virtually impossible to avoid expressing a point of view. Matthew Desmond, the author of Evicted, is no different. He wants to highlight what he sees as the structural defects of a broken housing system. In particular, he wants to emphasize the damaging effects that the system has upon the poor and dispossessed. So it's entirely natural that Desmond should be sympathetic to the plight of the people most affected by a chronic lack of affordable housing. We see this in his many harrowing depictions of the lives of those individuals trapped by a system that no longer works for them.
At the same time, Desmond tries throughout Evicted to be evenhanded in his approach. He strives to produce a scholarly work, one based upon a large body of empirical evidence. This is not an extended op-ed; its tone is academic, not polemic. That being the case, Desmond is not concerned with criticizing individual landlords for making money out of the system; it's rather the system itself that is the problem and needs to change. He further recognizes that landlords need to be part of the solution if meaningful change is to come.