I have seen many friends (non-muslims included) who take citizenship oaths only to say later it was just a formality and that they do not believe in it. Among the reasons they give is that the oath may require them to consider enemies of their new nation their enemies (which mostly means Muslim countries) and abiding by the nation's law which may support Homosexuality, Riba & other deeds deemed 'Haraam' in Islam.
What should my response be to such people?
For example, the oath of allegiance to USA in 2016 is:
"I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty, of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I will bear arms on behalf of the United States when required by the law; that I will perform noncombatant service in the Armed Forces of the United States when required by the law; that I will perform work of national importance under civilian direction when required by the law; and that I take this obligation freely, without any mental reservation or purpose of evasion; so help me God."