As for their assertion that this amounts to procuring grace for someone else, it is incorrect, because we say, each person who helps the Imam and strengthens his rule, enjoys a benefit specific for himself, may it carry expediency for others as well. It is like what you say about the apostles that their carriage of the burden of Prophethood and delivery of message to the public bears expediency for others. This requires the opponent to answer a query about “those having a say” - how is it that it is obligatory on them to choose an Imam for expediencies that encompass the entire Ummah and is it not requiring one to do something that benefits someone else? Whatever may be your justification with regard to the situation of the apostles is our very answer here.