First the law expressly forbids a patent on ideas.
As to the second half of your sentence, I am not sure if you meant execution is the hard part of having an invention or literally having capital to bring an invention market is the hard part. If you meant the later, I agree. Moreover, I think that is one of the strongest reasons for patents in most industries.
The Movie Flash of Genius provides a good example to highlight my point why patents are good and level the playing field for the little guy. Professor and part-time inventor invents the intermittent wipers for cars and brings his technology to Detroit only to have the existing car manufacturers simply steal his idea.
Kearns never intended to manufacturer the wiper much less manufacture cars to install his wiper, rather just license his awesome invention...that fits the definition of troll, but was he a patent troll? What if he did want to manufacture it, but simply didn't have the capital to begin mass production on the Detroit scale...would that make him any more or less a troll because of his subjective intent? Finally, if he did have the capital to actually take his wiper to market, in a world without patents why would he invest in bringing the invention to market when the big car manufacturers or existing wiper manufacturers are simply going to eat his lunch?
The whole concept of Apple, the most valuable company in the World, calling anyone a patent troll is crazy and basically the same corporate strategy the big car manufacturers used against Kearns, claiming his invention was obvious and just combinations of known prior art. Yet Apple and the big corps escape being consigned to being patent trolls themselves despite the fact that they hold more patents that are either complete bs or purposely withheld from the stream of commerce (like oil companies buying up alternative energy patents to keep them from coming to market). Like when Apple defensively extracted nearly $2 Billion from Samsung for violation of their rectangle with curved edges patent (which was subsequently over turned). Apple is sitting on over $200B in cash, they could have licensed or bought this patent, just as Ford and the others could have done with Kearn's wiper. But lets get serious, these are the same companies that determine if faulty parts should be replaced by comparing the cost of a recall compared to the projected cost of anticipated wrongful death claims. These big companies make the same calculated risk in stealing other people's intellectual property versus paying for it.
Perhaps the great irony of Apple's unwillingness to pay for someone else's invention, it forced Apple to innovate and ultimately produce a competing technology that didn't violate the patent. Moreover, this patent actually fostered innovation for a competing product, and while Apple and others may claim Apple's innovation isn't as good as the patented invention, it shows Apple's true colors where they aren't really claiming the patent is stifling innovation so much as stifling their ability to simply violate someone's better invention without paying for it.