I think what he is saying is that rather than abandon the GOP one should work to change it from within. I disagree that it is changable from within, I think it is well captured by interests not of its conservative roots. It's fine for wanting to move a party one way or another, and if the system is fair and open you have some ability at that. But I think the GOP and the Democrats have for too long been unchallenged as the dominate parties and have stagnated. Instead they are beholden to special interests and lobbiests and their goal isn't so much to push their agenda and platform, but rather to stay in power. So long as there are an unrivalable 2, that's accomplished.
The point about letting the liberals win is that if enough people left the GOP, it would loose too much of its base and it would be unable to capture elections. In such a case, what is defined as the greater evil then wins; the liberals will always get in since basically almost all national elections come down to a 50/50 split + noise. But enough base retention is necessary to keep the 50/50 so that the noise is what elections get based on. Without the 50/50, it's much harder for the lacking party to get elected. My point is that is exactly what you want, well at least now that the GOP has moved so far down the road of fascism. You may have to take some liberal wins to force the GOP back, and if you actively vote third party you can put even more pressure on by showing that you're not just a lost vote but you're a supporter of another team. So long as you don't go democrat, since your opposition will get lost in that mess.
In the end, the Republocrats represent the status quo. Either or, you're not going to get much difference. Which is why the Obama administration has thus far looked very similar to the Bush administration. Support of the status quo can't change the status quo. And if the status quo is evil, then you should be even more opposed to supporting it. Changing from within is dead. The only way to change the GOP is to make it unable to win elections, as their main goal is maintaining power. That, or the best option is to replace it. Though that one is really tough in the selective, limited, restricted system the Republocrats have currently set up. I think it's good to change over parties every once in awhile. Keep them honest I say.