Practicality and the Second Greatest Commandment
He could have taken a tack more like the modern "Love your fellow man" (or, if you have to be PC, "Love your fellow person". I suppose if we were living in the time of Star Trek, it would have to be something more like "Love your fellow sentient entity"). As good as that sounds, for practical purposes, you actually have to choose some subset of the human race to love, as you can't practically love every one of them. The question is, how do you choose that subset?
You could just choose your friends and the parts of your family that you like, but, common as that is, it's rather obviously not what God has in mind.
You could ratchet things up a bit, choose one or more "oppressed" or needy people groups and love them, and consider that this gives you leave to give short shrift to loving others, particularly those you consider to be the oppressors of your chosen people groups. Common as this also is, it also falls short of what God has in mind.
God commands us to love our Neighbor as ourselves. A neighbor is simply someone who comes near to you (who is in physical proximity to you, who is close enough for your actions to affect them). This is not just those who live near your house, this is those who come near to you all through your day. If someone comes near enough to you that what you do affects them, you're commanded to love them as yourself.
Basically, God has taken the choice of what subset of the human race to love right out of our hands. If they're nearby, you're commanded to love them.
The bureaucrat who messes up your life by forgetting to give you information is someone you're commanded to love as yourself.
The policeman who gives you an undeserved ticket is someone you're commanded to love as yourself.
The person who cuts in line in front of you is someone you're commanded to love as yourself.
The political speaker who opposes your views, who you've come out to protest is someone you're commanded to love as yourself (N.B. that means you don't shout them down to prevent them being heard).
The white supremacist who disses you for being black is someone you're commanded to love as yourself.
The school principal who suspends your kid for bringing a plastic soldier holding a plastic knife to school is someone you're commanded to love as yourself.
The spammer who litters all of your posts with spam comments is someone you're commanded to love as yourself.
I think you get the idea. If I haven't managed to hit you with the equivalent of Jesus using a Samaritan as the 'good guy', please feel free to add your own examples.