"Commerce on the Internet has come to rely almost exclusively on financial institutions serving as trusted third parties to process electronic payments. While the system works well enough for most transactions, it still suffers from the inherent weaknesses of the trust based model. Completely non-reversible transactions are not really possible, since financial institutions cannot avoid mediating disputes." https://bitcoin.org/bitcoin.pdf
Personally, I want a trusted third party to mediate disputes. If transactions are completely non- reversible, and there is no, dispute, mediation, or remediation possible, the need for trust does NOT go away, it just shifts so that you must trust every entity you transact with.