As the Charedi Population gets larger and larger, there will be less non-charedim to support them.
Fairly soon (20-30 years) they will be the majority of the population and in about 50 years they will be around 75% of the population.
How much can the charedim physically pay, how much taxes do you expect them to pay, You cant expect someone to pay over 50% of their income to a non-working segment of the population. They will balk at paying and for those who say to force them to pay, they will just leave greatly speeding up the demographics.