There are so many religions and believes on the face of the earth, and people have all the right to make a choice about who to worship.
There are so many people I have met in my life time, and I respect their decision concerning their religion or beliefs. Some practice Christianity (as I am) and worship in churches, while others practice Sikhism, Hinduism, Buddhism, Shinto, Judaism, Islam, Babism, etc.
Courtesy demands that you respect the religion of others, by so doing you gain their (persons of other religion) respect too. Otherwise, whatever you say to them (persons of other religion) regarding another religion besides theirs, will definitely fall on deaf ears.
Bottom-line: Never ever allow yourself to become very critical of people of other religious beliefs besides yours. If they (persons of other religion besides yours) do not seem to comprehend your religion or beliefs, leave them alone. Would you?