I think Mormons are more relaxed about dissent because their church has made a better effort at countering criticism and addressing difficult topics than Watchtower. So if someone stands up and complains, there is an attitude, “we’ve heard all that before, it’s old news”. Whereas if a JW speaks up about 607, Rutherford, UN, Malawi/Mexico, two witness rule, blood, and the rest, many JWs are going to be like, “say, what!?” And look in vain for official Watchtower responses.
Over the past few years the Mormon church has made efforts to produce official responses on controversial issues such as historical polygamy, racism, character of Joseph Smith, dubious Book of Mormon history and so on. Mormon missionaries are now generally at least aware of most controversial topics, so they don’t come as a complete surprise if confronted about them. Even if they can’t defend the points themselves, they are satisfied that the church has provided an answer to criticisms.