The paper never insists that irreversible transactions are the ONLY acceptable form of financial settlement. In fact it says "the system [financial institutions] works well enough for most transactions".
It points out that there is NO electronic system that allows no reversible transactions, as you can with cash. That's why it's titled "Bitcoin: A Peer-to-Peer Electronic Cash System". The author wanted something similar to cash, but electronic.
Besides that, discrediting a paper just for the introduction, which is just the opinion of the author regarding why they think such paper is interesting, is short sighted in my opinion.
