Contradiction with Proverbs 24:17
Rejoicing when your enemy falls contradicts with sympathizing and sharing in others' emotions, as Romans 12:15 encourages empathy with both joy and sorrow.
Proverbs 24:17: Rejoice not when thine enemy falleth, and let not thine heart be glad when he stumbleth:
Contradiction with Ecclesiastes 3:4
Suggests a time to weep and a time to laugh as separate, whereas Romans 12:15 emphasizes simultaneously rejoicing and weeping with those who do so.
Ecclesiastes 3:4: A time to weep, and a time to laugh; a time to mourn, and a time to dance;
Contradiction with Matthew 5:44
Commanding love and prayers for enemies who may cause sorrow conflicts with the straightforward emotional sharing of Romans 12:15.
Matthew 5:44: But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;