The biggest reason that you don't hear about Mormon Soup Kitchens is that the LDS Church has a different way of providing support for the needy. Every month, faithful LDS members fast and pray for a period of about 24 hours. They then donate at least as much money as they saved by not eating during that period in the form of fast offerings. Members who don't have money, such as farmers in third-world countries, can donate the food itself. This money and food is then used to provide welfare assistance, beginning within the boundaries of the ward or branch, with the surplus spilling over into more general funds until it can be used the world over.
Welfare from the LDS Church is distributed under the direction of local bishops or branch presidents, who can call on the resources of the so-called Bishop's Storehouse to provide food, money, and other necessities to those in need. Such welfare is extended to members and non-members alike, but is not given as a dole. Except in very particular cases (e.g. a widow who has no family to support her), church welfare is viewed as temporary assistance, not a permanent commitment. It is only to be used long enough for the person or family to become self-supporting and sustainable. People who accept welfare from the church are also generally required to do something to in some sense earn the goods they are receiving. For example, an able-bodied man may be asked to do yard work for a local widow each week. He may be receiving far more assistance than a few hours of yard work would fetch in an open market, but it gives him the dignity of feeling that he is doing what he can to give back. It helps to avoid giving the recipient a sense of entitlement.
The last time I went to the soup kitchen, one of the volunteers there mentioned that they used to require the homeless people to help out with either the serving or the cleanup in order to qualify for the free food they were getting. But the ACLU caught wind of it and sued them for slave labor, and so they had to rely on volunteers for these duties instead.
The local LDS leadership helps to furnish these volunteers by assigning each ward to provide a certain number of volunteers in a rotating fashion. The man running the soup kitchen told us that if it weren't for the support of LDS members who volunteer from wards around the valley, they would have had to close shop a long time ago. In addition to providing manpower, the LDS church also donates food to the soup kitchen.
So if someone tries to tell you that Mormons aren't charitable because they don't start soup kitchens, just remember what Atticus Finch says: "You never really understand a person until you consider things from his point of view, until you climb inside of his skin and walk around in it." It is easy to overlook the many, many good deeds done by the LDS church and its members, largely because many of these deeds are done quietly, without the left hand knowing what the right hand doeth. I have learned more and more that what someone says about other people tells me far more about the person speaking than the people he's talking about.
Or I suppose you could follow Jack Handy's rule: "Before you criticize someone, you should walk a mile in their shoes. That way when you criticize them, you are a mile away from them and you have their shoes." ;-)