Depending on where you live, the Salvation Army might be the only place in town where needy people can turn for help.
I think most people tend to think "any port in a storm." If they are really needy, they will get help wherever they can.
And if, in our communities, help usually comes from the Salvation Army or the Methodists or the Baptists, there is no harm in helping the needy by contributing to those causes.
I live in an area of the country where Catholics are only about 5% of the population and the Catholic Charities offices are almost 200 miles away.
If I see hungry people in my community I am not going to say, "Oh, the Salvation Army helps the hungry here. I'm going to help the hungry 200 miles away."