While stealing from anyone is bad, Yes it is much worse to steal from the poor due to how their ability to survive is impacted. The wealthy have more resources to fall back on, where the poor would not be able to provide basic necessities to survive.
For example, someone steals a wealthy mans car. He is wealthy, he can afford to call a cab, and afford another car. You steal a poor mans car, he cannot afford a cab home, he cannot afford another car, he can lose his job since he cannot get to work. He can die in the elements trying to walk to safety somewhere, he can die from starvation not being able to get food or even go to the office to even apply for food stamps. He cannot feed himself or his family without transportation, and in many areas there is no such thing as public transportation it doesn't exist at all.
The poor survive on everything they have to survive, the wealthy do not, and more often than not the wealthy cannot understand what it is like to not be able to afford food, shelter, transportation, electricity, water or sanitation services. You cannot compare the tow equally.
I disagree that stealing is stealing. For example, a guy who is stealing baby food to feed his child because he has no money is stealing out of desperation to care for his family, that is not the same as a teenager stealing a Ferrari for a joyride. Those cannot be compared.