"I won't support X until I see an example of X in the world" is a classic Catch-22, because how can X occur unless people first support it? If no one believed a new thing was possible until they had seen an example of it in action, there would never be any progress.
I'm not sure what you mean by a "focused, realistic discussion on taxation" or why you think such a discussion would be difficult for this group. Evidence for the viability of voluntarily-financed government includes the following:
• Any legitimate expenses of government are a tiny fraction of what government spends now, so the system would only need to bring in a relatively small percentage of the present tax take in order to work
• The elimination of coercive taxation would be such a boost to the economy (no more time and effort wasted trying to evade or figure out taxes) that people would tend to be much more financially able to donate
• People at present voluntarily donate billions of dollars a year to all kinds of causes that overlap with things that government does -- health, charity, science, the arts, etc.
• Most members of society think government is necessary and many are fearful of a world without government, so these beliefs would strongly incentivize them to voluntarily support government in order to make sure it didn't disappear
• Even some freedom-minded opponents of government would likely donate just to prove that the voluntary model is viable and prevent society from regressing to a coercive model (I would)
I'm not sure that most church tithing occurs because people think they would go to hell if they didn't tithe. Public pressure could certainly be a motivating force to get people to voluntarily donate to government. Businesses and other organizations might offer discounts, perks, etc., for those who could provide proof of having paid taxes, prominent public figures who didn't pay might be publicly shamed or embarrassed, etc.
Love & Liberty,
((( starchild )))