Do you think we could maintain a clean environment without regulations, just based on personal responsibility?

No, because people suck. Unfortunately, you can not rely on people taking the 4 extra steps to a trashcan to throw out their garbage, and you definitely can't trust a multimillion-dollar corporation to make decisions for the good of the environment because doing so usually costs them money, and all they care about is money. If killing the environment will fatten their wallets, then they won't just kill it, they'll eradicate it from any sense of prior existence.