Now for the next penny to drop.
No income tax advantages for married people over singles. Why redistribute wealth towards a traditional social model or a newfangled one? Why favour a nulliparous married couple over a single mum in their period of economic hardship?
Instead, raise tax relief for people with minor children. Or give everyone relief on an equal basis.
And marriage tax benefits ain't any more just than offering tax relief to home owners - thus redistributing wealth from renters to buyers.