No pope should ever kiss another religion's "holy" book because there is no other Holy Book other than the Bible. While we cannot know what was in his mind when he did it or if he even thought about the implications, that photo to this day would have potentially aided the now non-existent "Devil's Advocate" to stop or slow the canonisation of John Paul II.
No pope should ever visit a mosque. Benedict XVI did this in his visit to Istanbul, once known as Constantinople. While in the Blue Mosque, he stood holding his pectoral cross, He did not bow his head, nor did he pray in contemplation. He could be seen moving his lips, perhaps invoking the Lord's Prayer or a blessing to convert the Mohammedans, one can only hope.
No pope should ever pray in a mosque with head bowed and eyes closed as Pope Francis did. By doing this, one is creating scandal and affirming heresy. Islam has been called the "worst Christian heresy" and has been condemned by many Saints. While modernists suggest that they "profess" the God of Abraham, at best they have a distorted and false view of the Triune God and at worst they worship the ancient god of the moon (hence the crescent) which was the norm throughout Arabia.
Did I write, "no pope should ever visit a mosque?
On other note, when we go to greet our host in his house can we dress for the occasion?