One of the reasons that criminal cases require proof "beyond a reasonable doubt" is that the government has many other advantages when it brings a case to court, and raising the standard of proof serves to offset some of those advantages, thus promoting balance. Further, since citizens are supposed to be the masters and government the servant, any imbalance should favor the citizen.
In a civil case between non-government parties, it's generally fair to reduce the standard of proof to "preponderance of the evidence" because--at least in most cases--the government's "advantages" don't translate into advantage for either party; to require a higher standard of proof would be to put the citizen who happens to be the plaintiff in a particular case at a decided disadvantage compared to the one who happens to be the defendant.
I see no reason, however, why the lower standard of proof should apply in cases where the plaintiff is, in fact, the government. While it may seem in some measure reasonable to have a lower standard of proof in cases where money is owed for reasons not involving wrong-doing, a serious difficulty would arise in cases where a person refused to pay and was ultimately charged criminally for such refusal. If the person never legitimately owed a certain sum of money to the government, the person cannot justly be prosecuted for refusing to pay that which was not owed. Thus, prosecution for non-payment should require proof beyond a reasonable doubt that the money was, in fact, owed. To allow a lower standard of proof in non-criminal hearings would create some awkward situations where the government would be found to have the authority to demand payment but lack the authority to punish non-payment.
Excellent (and fascinating) point.
Although, I understood that the difference in standard of proof was one of the reasons why asset forfeiture was such a popular way to steal stuff from their supposed “masters”.
Perhaps pushing to have reasonable doubt applied to asset forfeiture cases would help curb some of the abuses.