Retroactive Elasticity (a continuing series)

A truly amazing paragraph authroed by Robert Rubin found in a Wall Street Journal article:

From "Bring Back the Estate Tax Now"

Ordinarily in tax matters, the effective date would not precede the
date of enactment, or at least the date that a measure was introduced, because Congress knows that taxpayers make their plans based on the existing code. But in the case of the estate tax, presumably nobody's demise was affected in timing by the structuring of our tax laws. And importantly there has been notice—through the president's budget and statements by public officials—that a tax would be enacted earlier this year that would apply to the whole of this year.

"Notice" and "statements" by public officials are enough to legitimize a retroactive tax?

I disagree. This would usher in a very slippery slope concerning which "statements" could usher in new taxation (and other legislation) retroactively. Furthermore, what "statements" (and by whom) effectively satisfy this "notice" standard that Mr. Rubin has put forth?

In addition, Mr. Rubin ascribes a "planning" component that serves as the main obstacle for establishing a retroactive tax, as if to say that the ability of the taxpayer to "plan" paying his/her taxes serves as the only obstacle in legislating retroactive obligations. But the real economic loss of paying taxes is not merely offset by the ability to "plan" for them. This is bad policy.