The atheists who help others don't have to advertise and don't call themselves "missionaries." The Socialistic practices of taking care of your people at home that are practiced in Denmark, Switzerland, Germany, and France are great examples. Doctors Without Borders is a great example of people going into a "squalid" condition for little monetary reward-and it is not a "mission." There is a group here in the US called Atheists Helping Homeless, as well as all of the Environmental, Animal rights, and Social Justice groups (The Innocence Project, Amnesty International, etc.) that aren't religious.
By the way, when born-again Christian George W. Bush was not adequately helping the Katrina victims, Hugo Chavez offered to supply electricity free of charge-and the christian wouldn't let him.
Actually, the objective of many of these "missions" is to keep socialism out of these countries-the Pat Robertson type of fundies will send people into a country to doll out a tiny bit of help in return for indoctrination into not only religion but also capitalism. Then we have access to their resources and their cheap labor.
And you can take that to the bank.