Is it permissible to use the plural pronoun to refer to a singular individual, such as "we went" and "we walked," and is the objection of some to this, on the grounds that it is self-aggrandizing, valid?

This Arabic style is not to be disavowed for its speaker, unless arrogance and self-admiration are observed in him, in which case he should be advised. The proof that it is not to be disavowed is its establishment from the Prophet, peace and blessings be upon him. Ali said: "The Messenger of Allah, peace and blessings be upon him, commanded me to oversee a camel for sacrifice, and to give its meat, hides, and coverings in charity, and not to give any of it to the butcher. He said: 'We will give him from our own [money/resources].'"