Why Do We Front Our Ideas?
"Preaching to the choir is unnecessary, and if you were to attain the age of a Methuselah you would still not be near converting your opponents. So what's the use of your arguing and asserting?"
This is a text-book example of a False Alternative. For there is a third reason to argue and assert, namely, to sway the fence-sitters whose number is legion, and to bring them over to our side.
What's more, it is false that preaching to the choir is unnecessary. We do so to reinforce them in their 'faith' and prevent their backsliding. It is also false that it is pointless to engage our opponents. We 'preach' to them for several reasons: (a) to change the minds of some; (b) to get our opponents to appreciate that we have a position that is rationally defensible even if not ultimately acceptable to them; (c) to oppose and demoralize them and make their arguments look bad so that their influence wanes.