Just a quick math to show why breeding carriers is OK:
Let's say A is gene for DM or dwafism - single gene disorder. The form A is normal, the form a is mutant. So AA is clean, Aa is carrier and aa is affected (on the level of genome, in case of DM it does not have to show).
If you combine carrier Aa with clean AA, you'll get these possibilities: 50% AA, 50% Aa. So no pups will be affected and any pup has a 50% probability that it is a carrier, but also 50% probability that it is clean!
If you combine two carriers, you'll get 25% AA, 50% Aa and 25% aa. But, in dwarfism, some dwarves die before being born, in DM not all affected animals actually get sick. So any live-born pup has a 50% chance of being carrier, 25% chance of being clean, and less than 25% chance of being affected and sick. If you have a rare bloodline, even combining carriers might be more beneficial to the whole population, than loss of the genetic material. The dog may be DM carrier, but it may also be, at the same time, clean for dwarfism, or other genetic disorders...
The more disorders you can test for, the more difficult it is to find good combinations, so it is important to keep in mind that sometimes the risks should be taken, and although it is very sad if a pup is born sick, it is still more sad if no pups are born at all.
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