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If an IRS audit disallows the § 419 plan or the § 412(i) plan, not only does the taxpayer lose the deduction and pay interest and penalties, but then the IRS comes back under IRC 6707A and imposes large fines for not properly filing.
Insurance agents, financial planners and even accountants sold many of these plans. The main motivations for buying into one were large tax deductions. The motivation for the sellers of the plans was the very large life insurance premiums generated. These plans, which were vetted by the insurance companies, put lots of insurance on the books. Some of these plans continue to be sold, even after IRS disallowances and lawsuits against insurance agents, plan promoters and insurance companies.
As the IRS started going after 419 and 412i plans people started selling captive insurance and section 79 plans.