There is a concept of "Eid echad ne'eman b'issurin" which means if a person testifies on something that is questionable we believe him. An example would be regarding kosher: if I go to a friend's ...
Is there a halachic reason to be opposed to Uri L'Tzedek and Tav haYosher? Why do some frum Jews oppose it? Really the only things that I can find is that Uri L'Tzedek is left-wing and led by YCT ...