Republicans believe that they're somehow "stealing" your hard work. The GOP ascribes to a selfish idealogy where people "deserve" all the money they earn, and the thought of the government taking money from them repulses them.
In addtion, they also have that whole flawed Reaganomics economic policy where cuttig taxes will make the rich wealthier, and somehow this will trickle-down to the lower classes. It DOES make the rich wealthier...but that's it.
The funny thing is that I think that notion (cutting taxes leads to higher tax revenues) can work, because the lower marginal rate encourages people to earn more, but only if the initial rate is high enough, and so there is some optimum. (Basically, at 0% there is no tax revenue, and at 100% there is no revenue because it's not worth it to anyone to earn anything, so in between there is an optimum.) Reagan's advisors, however, thought the rate at the time was above the optimum, when in fact it was below, and thus by cutting taxes they cut revenue.
Trickle-down, however, is just stupid.