You won't see that headline even though it is a very plausible explanation of their actions. The reason is that newspapers will say that we can't know the motives of politicians. 

That is a good practice for newspapers to follow, but unfortunately, they don't. During the tax debate, there have already been any number of stories that have told that us that Republicans "believe" that their tax cuts will boost growth or that they are proposing tax cuts "in order to" revitalize the economy. For some reason, they are fine with attributing motives when the effect is to put these politicians in a positive light, even if they refuse as a matter of principle to attribute motives when it would reflect poorly on them.

Of course, Republicans do say that their motive is to promote economic growth, but let's imagine for a moment that their true motive is making their wealthy contributors even richer. Do we think Paul Ryan will announce his latest tax cut proposal by telling the public how much it will give to the Koch brothers and the Mercers?

That doesn't seem very likely. He would instead make some claim about how the tax cuts benefit the public as a whole, regardless of how implausible it might be.

And in this case, it is pretty implausible. At best tax cuts can have a very modest impact in boosting growth. The best analysis of this issue was done by the Congressional Budget Office in 2005 when it was headed by Douglas Holtz-Eakin, a Republican economist who was the chief economic adviser to Senator McCain in his presidential campaign. His analysis found that using the most favorable set of assumptions, additional growth could temporarily replace one-third of lost revenue. This revenue increase was largely offset by slower growth in the longer term.

So accepting the Republicans' claims as to their true beliefs also requires accepting that they believe something that is not true. While this is possible, instead of engaging in speculation that assumes Republicans are ignoramuses when it comes to the economy, why not just stick to reporting what they say?