Beef can be hard for even healthy people to digest... and, if the stock from which the beef originated had johnes disease.. well, the jury is still out on that whole issue. But there are plenty of other confirmed nasties one can get from undercooked beef that makes it a poor choice whether you are ill or not. Only thing of it is.. I'm not a vegan, but I loved my veggies, but now my diet is pretty restricted when it comes to vegetables, and I recently had me a very severe case of low iron. I took iron supplements, but I also forced fed myself more beef. Whether one or the other, or a combo of both, I improved.
Guess it's like everything else in life.. in moderation, and properly prepared.