How did Jacob Riis change America's morals?

It is hard to make the argument that Riis, by himself,
changed America's moral values.  However, the "muckraker movement," of which Riis was a
part, certainly changed American attitudes towards social
problems.

During the late 1800s and early 1900s, Riis and
other muckrakers did a lot of work to expose social ills to the general public.  Riis,
for example, used his journalism and photography to show the plight of immigrants in big
US cities.  By exposing these conditions, Riis and other muckrakers made people more
aware of the problems and helped make them care about such
things.

The muckraking that these people did helped to
change American values enough that the Progressive Era was made possible.  People
stopped thinking that these social ills were inevitable and instead thought that they
were wrong and that the government should do something about
them.