Hello.
This is an interesting question and one I've had to think about recently too.
I came to the conclusion that really to me it's about how human beings choose to express spirituality.
Some do it quietly by themselves perhaps through thought and deed, while others seek and sign up to the reassurance, structure and rituals of religion or other organised belief systems (Catholic, Islamic etc).
My view is that so long as there is tolerance (and I know this identifies me as a softy liberal) and each person has the freedom to explore their spiritual dimension in a way that causes others no pain, then that's fine.
I would add that I'm also an advocate of keeping a person's options open as long as possible, so they can decide on what they believe is important and how they want to express their spirituality.
Of course what I mean is that I feel children are indoctrinated into particular religious systems very early on. Depending on where you were born, you're more or less likely to be a Hindu, Muslim, Christian etc.
This 'get em' while their young (and vulnerable to suggestion)' approach bothers me as it seems to preclude people gaining knowledge about what might be possible in religious and spirital terms, so they can make an informedchoice about what they believe and how they express this.
Many of my friends are Catholics and were indoctrinated so early on in life that the Catholic faith and way of doing things goes almost DNA deep. The way they engage with or apprehend the world - their bahviour patterns - is mediated by their early life immersion in Catholicism sometimes for good and sometimes for ill. Catholocism was part of their formative experience and it's influence is especially pertinent when it comes issues such as how people can labour under burdens of guilt and shame and become self-hateful as a result.
Also - and please note I have no evidence to back this up - my reasons for being pro-ploytheism also come from thinking that a polar or non-diverse view of how spirituality can be expressed leads to a blinkered image of the world. If dialogues around spirituality are prematurely closed off and a narrow view of how people should express their beliefs is allowed to grow unchecked by discourse that challenges this and which promotes a plurality of 'ways of believing', then fanaticism with the adjunct of a religious war can be a result.
Ahem.
So if I had children (sadly at the moment I do not) I would want to protect them from what I see as a monotheistic and limiting approach to spirituality - to give them a range of ways of thinking about their beliefs and ways of living - so later, when they are more cognisant of the world and have better self-knowledge, they can make up their own minds and choose. For example, I would want them to know about the works of people like Richard Dawkins, as well as Thomas Aquinas, so they could get a good hit of 'God the wonder, God the mystic force' and a good hit of 'it's crackers to believe in a Super Being, or so if God invented the universe who invented God?' dialogues.
So, to come back to the question of choosing relationships based on beliefs, well I think if you're tolerant and if whoever you're with is too, then everything's cool. However, if there is the slightest hint that your children are to experience a one-side view of how spirituality is expressed, I'd advise you head for the hills!
Best
Alex