The "Useless class" question has always existed, as already highlighted, the uptake in employment by newly arrived migrants is very low. The question remains, why add to the useless class ?
As for paying taxes, the clue is in the title - tax payers. They are people who have the skills and, in the case of migrants, a willingness to embrace the values of their new home and do what they can to make the best of their lot . In the case of corporate tax payers, they too contribute based on individuals who are employable.
There are various reasons for encouraging migrations. In France, the migrant has replaced the worker as the "hero" of the Left. Workers now vote for le Pen because the Socialists are too busy doing deals with islamic organisation here and there to secure the moslem vote. The working class suburbs of North Paris that used to be mostly held by the Communist Party have now all fallen to the deadly mix of Socialists and islamists.
As for the useless class, a new one is in the making, people who were not permanently on the dole but who held low qualified, low paying job. These are the next to go.
Regarding taxes, the few remaining workers of the 2060s can't be asked to pay the pensions of the huge number of retirees they will have to support. Another pension system has to be set up.