It's a good, better, and best mentality.I don't know everything about the LDS Church - but isn't one of their main claims that they are different from mainstream Christianity?
LDS Christians obviously acknowledge that other folks are Christians too - each person's relationship with Christ is something to celebrate. That is a very good thing. But it would be better and/or best with more correct doctrine (there all disagreements there, like all throughout Christianity). Also having a formal Church structure with prophets like those in the Bible to help people come even closer to Christ. So while acknowledging the good the Christian churches do, the Church of Jesus Christ of Latter-Day Saints does believe itself to be Christ's one true church on the earth.