• a Hindu marries a Hindu,  
• a Hindu marries a Christian 
• a Hindu marries a Sikh  
• a Hindu marries a Bengali, etc etc 

But why isn't it ok if a Hindu marries a Muslim, or a Muslim marries a Hindu ?

Why is there this barrier, why should two people who love each other not be able to live together. Is it the society ?, or is it because the next generation of Muslims (now) are totally brainwashed and totally illiterate and backward ?, answers please ....

The way the question is put, it sounds very simple, however, the more pertinent question is would a marriage between a Hindu and a Muslim, or a Hindu and a Christian, or a fascist and a communist, or a Labour and a Tory MP, etc. stand even half a chance to last and survive? Probably not. Like all ideologies, Islam is exclusive in some of its claims and cannot accommodate their negation without resulting hypocrisy and foul compromise. So a marriage between two people of competing religious beliefs or ideologies would only work if neither of the two partners really believed in their creed, but simply called themselves by that label. In other words, the inter- religious mix described in the question presupposes a secular society where religion is of no more importance than a preference for a particular kind of food or fashion.