We Tend to Be Too Hard on Our Own

Within Christianity, Mormon theology is one of the most expansive, "universalist" in existence. Our entire structure of temple ordinances is based on the idea that absolutely anyone can "pass the test" regardless of the religion they believe during this life - or even if they are hard-core atheists.

It's also not correct to say that such universalism applies only to some degree of glory but not the Celestial Kingdom. Absolutely everyone (minus a few Sons of Perdition who are the exception that proves the rule) will receive salvation within Mormonism simply through the Atonement of Jesus, so temple work can't be about people qualifying for the Telestial Kingdom - or even the Terrestrial Kingdom, since that essentially is the same place just with nicer people. (Seriously, that's the best description of the difference I've ever heard.) It has to be about opening the possibility of the Celestial Kingdom to ALL - making sure ALL have a chance to pass the test, if you will.

The difficulty is that we tend to be harder on our own than we are on those we don't know. The standard is the same, but we tend to think those who have been in the Church have had their chance while those outside the Church haven't. We forget that we aren't judges of final rewards. It's one of the most deeply ingrained "natural (wo)man" tendencies that exists, and, as a result, it exists in many members and, thus, within the LDS Church - but it's not part of pure Mormonism. I believe it's REALLY important to understand that. 

Sure, too many members don't get that fully, but it's there in great big font and blinking neon colors within the theology itself.