Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
By visiting the graves of non-Muslims, we can think of our destiny. It may even inspire us to strengthen our faith so that we are motivated not to allow ourselves to go astray and die in a state of disbelief.
In responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Visiting graves: Why?
Visiting the graves is prescribed for twin purposes:
First, to serve as a reminder for us so that we know death is our destiny and like the person or people who are buried in the graveyard, and sooner or later, we also will join them.
A second purpose is to pray to Allah to shower them with His mercy.
Visiting non-Muslim graves: Allowed?
In the case of visiting those who chose to reject the truth, we should leave them to accept the responsibility for the choice they have made; Islam does not permit us to force them to convert; likewise, it would be wrong to impose something on them which they never chose to believe.
It is like forcing someone to pray when he mocks the prayer. It is of no benefit to such a person.
As for the first point we mentioned, it does apply here:
In other words, by visiting their graves, we can also think of our destiny; it may even inspire us to strengthen our faith so that we are motivated not to allow ourselves to go astray and die in a state of disbelief.
Almighty Allah knows best.