That assumes that you actually *care* about what happens to other creatures - after all, you can generally get twice as much out of something if you work for your benefit at its expense than if you work for mutual benefit.
Now, I do actually care about how other creatures feel, because I'm all compassionate like that... but I don't think it's a very good basis for a moral system, because as soon as someone says "It's in pain? So what?" you run into a huge problem that undermines everything you've built up from that.
I prefer my base, where harming others means others harm you, so it is better to not harm others at all, which works for almost everybody because almost everyone has a modicum of self-preservation. Furthermore, it hits where it counts, because the kind of person who screws over others is most likely going to be doing it for their own benefit, and this system directly addresses that. It's worked for thousands of years, as well. True, it suffers from the same problem, in that it assumes that you care about yourself, but in practical terms it is more likely for someone to care about themselves than about some other entity that *isn't* themselves.
Just a thought. Not exactly a disagreement, just a difference in method in coming to the same conclusion of not harming others. Because, you know, I do actually think about these sort of things... when it's worth my time to do so.