The problem is that the IRS uses "civil" when it suits their purposes and "criminal" when it suits their purposes. If they can throw you in jail for not doing what they want you to, by any reasonable standard, that is "criminal" law.
Try not paying your property taxes and see what happens to your home. Try not paying into social security. As a business owner, try not filing any one of the hundreds of forms required by the feds, state, and local governments.
Most government agencies have both civil and criminal statutes, not just the IRS.