@Opiam:
Do you think that "race" or religion can ruin a relationship?
I think we need to focus the question a bit: "Can difference in race or religion ruin a relationship?" It can; it depends on the people involved.
As for "race," different ethnicities have different levels of privilege in different societies. If one person in the relationship is of a privileged race, and the other is in a discriminated-against race, it's possible that one or both parties won't understand the experience of the other–or not be perceived as understanding. This can cause problems in a relationship.
As for religion, most countries (but certainly not all) are tolerant of religious differences. If the practice of a religion is very important to one party, and not to the other, things can work as long as there's mutual respect.
All of this assumes that a relationship has been formed. Some people will have a "going-in position" that they could not be in relationship with someone of a particular race or religious practice (or non-practice). That would filter out problems very early on, although if attraction develops after a casual hookup, people may need to revisit their initial judgments.
At the risk of going off-topic, it's not unlike a relationship between serodiscordant parties (one HIV+ and one HIV-). Quite often, an HIV+ person will assume that the HIV- party can't fully understand what it's like to be HIV+, and that can become a problem. This is becoming less of an issue as HIV treatment advances. (If you want to address the HIV+/- situation, I suggest starting a new forum topic on that, leaving this thread to the race/religion question.)