Managing your resources--making tough decisions on how to deploy your financial, tools, materials, and humans--to minimize the threat of failure and maximize the likelihood of success AND treating people kindly, humanly, and with respect are two different things.
It is YOUR definition that makes a resource a thing. Dictionary.com defines it as: a source of supply, support, or aid, especially one that can be readily drawn upon when needed.
That certainly can apply to humans.
The bottom line is, however, that managing is about the deployment of resources and behind many of those decisions are ones that can be quite inhumane. We are all different with different strengths and weaknesses, our collective performance varies, our individual performance varies, we are the least reliable resource of all resources, all of us can be replaced, and no project or company exists so that a human can have a job; it exists to make a product or service to make money or some other goal. We are simply one of the many enablers to achieve that goal.
It is cold and callous and we all want more loyalty and love from a company, but that only exists in HR literature designed to attract talent. It ends when you sign your contract.
EDIT: When you are managing a performance capability, your goal is to have repeatable, sustainable, and predictable performance. This means all of the enablers you use, the machines and tools, the availability of funds, infrastructure, environment, AND people, need to be replaceable, not unlike a tire. If a cog craps out, you reach into the drawer, grab another, screw it in, and turn the machine back on. Indeed with minimal variances, you can pretty much predict the same level of performance you had with the other cog. If John Smith craps out--quits, dies, gets arrested and convicted--you need to reach in the drawer....
Of course, it is much harder than that, but that's the mentality IF you want repeatable, sustainable, and predictable performance.
If you understand the performance curve, whether you think it is normally distributed or positively skewed, most of your human performance that you will likely get will be severely average. That is what the curve means. We, however, like to kid ourselves that we found superstars, and our hiring selection process continues to find superstars, despite it being statistically unlikely. But if you think about, superstars are the antithesis of repeatable, sustainable, and predictable results. That is because, if your superstar leaves (assuming you really had one), then the likelihood of replacing said superstar is quite low, leaving your performance capability suffering.
All this sounds like I dehumanize. Maybe it is. But again, I do not operate a project so that people have a place to work. If one does not perform, they get replaced just like a cog. And I turn the machine back on. If I happen to get a superstar, icing on the cake, but I do not rely on him/her. Because he/she will leave, die, get sick, get arrested, disappear.