The author doesn't understand what repudiate means, and therefore all the arguments are nonsensical.
To repudiate means, according to Cambridge dictionary "to refuse to accept something or someone as true, good, or reasonable"
So, when a transaction or email is repudiated, it means that someone is claiming that they didn't do it, despite the fact that it was done.
Non-repudiation is a characteristic of a system whereby a user of the system will find it difficult or "impossible" to repudiate that they did an action in that system.
So when the author claims in a title that "Non-repudiation of emails is undesirable" they are getting the words and meaning mixed up.
It is repudiation that is undesirable, and that's why non-repudiation is such an important characteristic of some types of system.