Since when? That is completely false and until someone provides actual proof, as in clutch after clutch after clutch with poor results, then it will remain so. There has been NOTHING to point to spider x spider being a bad pairing and I have in the past done that pairing with no issues and have seen many other clutches from spider x spider with no issues.
Well then you can go ahead and go for it until you get enough proof to satisfy youself. Ill be over here not producing lethal homozygous forms. Whatever works for you!