Why does the Bible speak so negatively about tax collectors?

These men were literal traitors. Understanding why tax collectors were hated in the Bible reveals the profound nature of Christ’s forgiveness. First-century publicans weren't just standard government agents; they were Jewish turncoats working for an oppressive Roman regime who routinely cheated their own neighbors to fund lavish lifestyles. While the religious elite viewed these corrupt officials as permanent enemies to be shunned, Jesus eating with sinners demonstrated that He came as a physician for the spiritually sick rather than a judge for the self-righteous. Ultimately, the biblical accounts of men like Zacchaeus and Matthew the tax collector prove that no one is beyond the reach of the gospel or the command to true repentance.

Source: www.gotquestions.org/Bible-tax-collectors.html