Question: Should one pay a sick visit to someone whom he hates as a mitzva of bikur cholim and as an exercise of overcoming his negative feelings, or can such a visit be counterproductive?

Answer: This question has already been dealt with in Shulchan Aruch (Yoreh Deah 335) where Rama rules that one should neither visit a sick enemy nor pay a condolence visit when he is in mourning lest his visit be interpreted as an expression of joy at seeing the sorrow of the one being visited and thus causing him pain rather than comfort.

Of course this depends on the degree of the enmity between the two parties. But another consideration has been raised by some of the halachic authorities. There is the possibility that the sick person may misconstrue the surprise appearance of his enemy as a sign that he must be mortally ill, thus causing his condition to deteriorate because of the psychological impact.

Perhaps the best idea is the one suggested by the Aruch Hashulchan. A message should be sent to the patient (or the mourner) asking him if he would welcome a visit from his enemy. If consent is granted the above-mentioned fears are no longer relevant and a visit is very much in order.