I disagree. No one has a crystal ball, but some things are more politically realistic than others. I don't think Roths will remain unchanged for 30 years. RMDs, account balance caps, and even sunsetting the program by forbidding new money entering the accounts are politically realistic ways the program could be reformed over the years. You can see an appetite for some of that in some circles, even today.
Just confiscating the money, or ending the tax advantages retroactively for past contributions, are simply not going to be politically realistic. Senators and Representatives would look at such a proposal and seriously worry about being re-elected, even if the program desperately needed some changes. If presented with such an option, even if they thought it met the needs of the day, their minds would immediately turn to grandfathering to cover their asses. Furthermore, there is no appetite for any of this in any serious policy circle today. There is no sign of it on any horizon.
In contrast: there is plenty of political will for making more people pay income taxes, even today. Any time you hear the talk like "broadening the base," or "flat tax," or "47%," et cetera, someone is longing to do something that a Roth account would hedge against: reducing or eliminating the share of the population that pays no income tax. Ie: the number of yous out there. Many a GOP hopeful has run on these principles. Consider Herman Cain, and his 9-9-9 schtick, which had him out at the front of the GOP primary for something like a month before the spotlight moved on. Moreover, Democrats love to compromise. If a GOP Presidential hopeful runs by turning people like us into the Welfare Queens of the political moment, and wins, the conversation will stop being about whether or not "base broadening" will happen and start being about what the price is.
It's not guaranteed to happen, but it's likely enough to try to get some protection against, especially if the cost is low.