Paying higher tax rate also result in less financial security in the household.This is what I find it's unfair for unmarried people that they have to pay tax cost greater than married people.
That's contradictory statement. There is nothing "fair" about coercive taxation at all. Acquiring someone else's private property by the threat or use of force and against the will of the owner is unjust and morally wrong. So to call coercive taxation fair is like calling rape consensual. And if fair is to mean equitable then any money stolen from citizens, in differing amounts depending on demographic, does not fit the definition of fair as we all commonly use the term, that is to say not the twisted Orwellian usage of the word by politicians