@christabelle Look up the Wikipedia pages for the each of the Big4. There's a controversies section for very good reasons.
They've been busted for widespread exam cheating in numerous countries (including on ethics), banned from auditing in a few, racked up fine after fine, been involved with bribery scandals, and accused of passing on confidential information about clients to insurers, banks and potential business purchasers, among other notable little issues. They're all still here.
The only questions are 1) how the idea of working for companies with track records like these makes you feel, and 2) can you find employers with no moral or ethical issues to work for, anyway?