My parents are convinced that the government will tax Roth IRA earnings in 20-30 years "when the government realizes how much money they're missing out on." As I am investing through my Roth I am obviously not in agreement with this paranoia, to say the least.
Of course given time value of money, the government is not 'losing out on money'.
I don't think they could get away with double taxing Roths though, worst case would be that they change it to a traditional tax treatment as some point in the future and gains up to that point are still tax free.
I don't see it ever being changed, as they are not really losing out on anything. They get their share one way or another.
I personally like the roth treatment because I'm investing with the anticipation that my income during retirement will be higher than my current income. It won't be higher than my peak working income, but it should be higher than the first 15-20 years of my career because during that period i am still building my investments up. Plus as mentioned it is a hedge against tax rate uncertainty.
time value of money is strong though, so it's not really an easy answer, even if you have a higher tax bracket at retirement than you do when working.