“what will keep them from just drawing from your account to enforce this law?”
In reality, Congress stripped IRS of most of its normal enforcement powers, hence collecting the Obamacare tax will be a challenge.
http://www.aei.org/article/health/healthcare-reform/if-you-dont-buy-insurance-will-you-really-pay-the-tax/
>>Even paying the penalty is effectively optional, because Congress, for political reasons, barred the Internal Revenue Service from using its most effective tools — liens, forfeiture and prosecution — to collect it.<<