Let's be quite clear. God acquits the guilty because Jesus took the rap for them. God declares us to be righteous on the basis of Jesus' righteousness, not ours, not even the righteousness that God produces in us. It is only by accepting God's mercy through faith in Jesus that we are saved. It's hard for us to understand exactly how hated a tax collector was.
Nobody likes paying taxes.
But the taxes WE pay are collected by public servants who for the most part do it honestly and are forced to do it honestly by law. The taxes they collect are used by the government, in theory at least, for the common good. Not so in first century Palestine. The taxes were collected to send to Rome, the foreign, heathen, occupying military power. The tax collectors were traitors to Judaism, cheats and extortioners, taking more than the legal amount and pocketing the rest.