alt Hacker NewsRight they (the politicians) don't actually think that, they just say that to get cooked projections. Once those revenue projections turn out to be false, it doesn't matter because they already have their tax cuts baked in. Then everyone can blame the other side for deficits and campaign on fixing it. Rinse and repeat.
Let's be clear and not do this both sides thing - by "they" we mean Republicans. You may not agree with their policies or what they want to spend money on, but Democrats (at least in aggregate) live in the real world where they acknowledge for the government to spend money they will have to raise taxes.
Republicans are the only party that in the 21st century acts as though we can simultaneously cut taxes and increase spending and everything will be fine.