Inbreeding, linebreeding, and outcrossing occurs in nature...with performance for survival being the selection method. Nature doesn't prejudge. It is not prejudice. There is no affirmative action or nurses saving the weak. Instead, it simply says...get er done or die.
As a result, each method of breeding is used in nature and when things get "out of balance" going "too far" with any detrimental trait, variation of a superior alternate phenotype (and genotype) is RIGHT THERE waiting for the oppertunity to bring things back into balance.