Let me rephrase to be more neutral. Imagine two genetic lines. Both lines have one bad mutation. Survivable, but makes the individual less fit. With asexual reproduction evolution has to pick one or the other. With sexual it can get rid of both.
You are not really thinking this through. How would a fitness reducing mutation become a feature of a genetic line in the first place in asexual reproduction? The "silent" partial carrier dynamic of genetic defects is a problem exclusive to sexually reproducing organisms.
How can sexual reproduction "get rid of them"?
Play it out for a few generations, you will see, there is a frequency equilibrium. We've done this in school with paper, but if you know some programming, it's an easy exercise. Anyway, unless being very detrimental for partial carriers, the bad allele is gonna stay in the gene pool.
A random mutation. Especially when combined with the founder effect or some other genetic bottlenecking.