No, it's not.
A few years ago in my Human Geography class, a girl argued that the US (or it could have been another country in practice for Model UN) should not send any type of aid to countries that are in need of it because, in essence, it's the fault of the government and/or people of that country.
It's their own problem, and we should have no hand in fixing it.
I believe that this is wrong for two reasons. For one, I think that people don't always have a say in their own destinies. In places where a tough government or military dictatorship is in power, people don't always have the ability to change things, or fix their own problems. Independence left many colonized countries in undertrained control and in poor economic conditions to start out with. That's not said country's fault, in my opinion.
Another reason has to do with our own security. If a country is stabilized, a region is stabilized. And this has to do with our own protection as well as protection of that country and region we help out. We give aid, and we get benefits indirectly. They may take time, they may not be definite or secure, but we can contribute to a greater good.
Some argue that foreign aid to third world countries amounts to "global welfare," and just props up failed systems of government or dictators, which just perpetuates, not solves, the problem. A lot of aid money simply lines the pockets of corrupt officials.
However, I think your point about world security is valid- the US does have an interest in ensuring the world is stable. That's the current justifcation for the monetary blackhole that is Iraq. Sure, the Iraq War was a terrible idea, but nothing we can do about it now- it's in our national interest that the country be stabilized and secured.