Choosing a Buddhist partner ain't beneficial to spreading Dhamma? Recently seeing questions on Buddhist stack exchange community I thought to ask this question.
My understanding that we can choose anyone as life partner the way Buddha said all about is kind of qualities and so on.
And Because of Buddhism is nothing but liberty that's why Buddha didn't impose this thing to followers just like in other religions.
So if it was like we should marry to Buddhist only then it were Dhamma's sake and would helpful to spreading Dhamma.
One another question is if both partners are from different religions then how they could lead their children?
May other partner have influence of it's own religion and may this would worse everything partner's child's and own life. 
I seen in other religion they are super religious to choose a partner.
Even my own experience my ex was a Muslim and she has great impact of religion on her since my thinking is being like that.
See we Indian mostly choose Buddhist to marry but absence of practicing Dhamma. 
So I'd choose the one who is Buddhist and practicing Dhamma as well then we could spread it well.
Finally since both are Buddhist then its kind of package we have got everything in it. All qualities and as Buddha's way to choose a life partner.
So why Buddha speak about qualities instead advising people to find Buddhist partner that could one of the way to spread Dhamma?
Thank you.
Choose a person with compatible generosity, compatible morality, compatible faith and compatible wisdom. That means even among Buddhists, you still have to filter out the potential spouses. 

Marrying a person of a different religion could be highly problematic if you are a practicing Buddhist. I have seen some people make it work, but those are mostly people who are simply Buddhist by birth and not interested in it much and don't care about what religion their children pick. So either you have to be that way or the other person have to be that way to make it work.