Actually, a better question for the OP would be this: Are you REALLY trying to accomplish something of a personal nature here or did you start this post just to engage in academic discussion? I'm sorry but I can't help suspecting the latter option.
The OP is not really sharing why he so desperately wants country X's citizenship and that's fine because it's largely irrelevant. I actually looked into citizenship laws for most countries a couple of years back, just out of curiosity and, with minor quirks here and there, they mostly run similar to each other.
The common theme to most countries is that there is no ius soli citizenship (i.e. citizenship just through birth in the country alone), unless this would leave you stateless -- e.g. parents are unknown, or you can establish that you don't inherit either of parents' citizenships.
However, from my research, I don't recall seeing a single case of a country that won't grant citizenship to a child born on its soil to parents who are both citizens of that country as well. I'm fairly certain in this case the child would have an automatic right to citizenship in that birth country, and it's completely irrelevant that he/she also happens to acquire another citizenship at birth. Because of this, I have good reason to suspect the OP is just engaging in academic discussion here, not trying to accomplish anything difficult or complicated.
If I understand the situation correctly (child born in country X to citizens of country X) and if what the OP is saying is true: that country X's authorities have told him they won't grant the child citizenship if he/she also got another citizenship, then I'd tell the OP to dig higher up the chain of command in his country because those 'authorities' either didn't know what they were talking about or think it's ok to just make up their own law at the spur of the moment.