No where does Christ teach that it is just to compel others to “share” their wealth. There is no compassion when one is compelled. The one required to share is not acting from love, but from compulsion, even if they are in favor of it. Those who compel or support the compulsion are not acting from compassion, but from power, even if they feel it is necessary.
We can claim that taxation to help the poor is necessary in an otherwise free society (leaving aside the constitutional issue of the central government ding it), but we can claim that the participants, the taxed or the government, are performing any act of compassion or charity.