That's the whole point of the tax bill (I mean on the individual side, since the real money is all on the corporate side). It lowers rates but increases the amount of income you pay taxes on by taking away your deductions and exemptions. It temporarily increases the child tax credit and standard deduction in order to soften the blow, but they ultimately need to repeal that softening for normal families in order to fund lowering the tax rate in the top bracket.
I don't agree that the point of this bill is to increase taxes directly on the majority of income earners.
I say directly because one clear desire the republicans have is to cut major social programs while not giving us break on payroll tax which in an of itself is a tax hike. Also the new breaks are not tied to inflation like today's personal exemptions which makes them more risky bets long term. Granted over the 8 year period I don't expect inflation to impact the value much but again long term its not great.
The temporary move is a clear dodge of their own senate deficit hawk rules to try to bullshit the true cost of this legislation to get under the 1.5 Trillion dollar estimated loss. Cynically the Republicans could be doing this knowing there will be a huge income loss and growth wont fill the void, but its a short term win. A glass half full view may be some Repubs still believe that the estimates are wrong and growth will fill the void. Thus allowing an easy continuation of the breaks.
The reality is though that this creates a guaranteed budget battle for whoever is in control at that point . They will be forced to renew the breaks or be blamed for a large middle class tax hike. I find it unlikely the future congress wont find away to extend these, given the inventiable blow back. The downside is I am sure some shitty provisions will be pork barreled in with it.
Still though, your fears are valid that compared to today's long standing tax code, this leaves a none zero chance that 8 years down the road a baked in tax hike will hit the majority of American households.
Oh and side note. I am not sure wtf happened to, "We are going to simplify taxes" but this legislation just made taxes even more convoluted and challenging. Fear not Intuit and CPAs your jobs are safe. Granted I am not a fan of simple tax codes anyway.