First off, I'm not an "R" or a "D".  
I won't put my faith in a government, union or other group to take care of me.  I am a grown man.  I am capable.  I don't have my hand out begging.
What gives you the right to the fruits of my labor and sacrifice?
If you have a tribe where 10% of the population does the hunting while the other 90% sit around the campfire, yet everyone shares equally in the food, eventually the hunters lose.  As time goes by there are less hunters.  Why go out and track down game when you can sit around the fire and get just as much food as everyone else?
Why punish success?  Why am I greedy for working 80+ hours per week when someone else gets a government handout?  Why should I continue to work 80+ hours when I won't get to keep half of what I earn?
For that matter, why should I hire anyone?  I'm hiring someone in September.  I plan on hiring at least 5 more people before April.  Why should I take on the extra risk involved and get hardly any benefit?
Please, answer those questions.
Because it's not punishing success. It can feel Marxist (from each/to each), but progressive taxation is the only fair way to go about providing for a modern society. For example, you're a trucker, would you really want to operate without the interstate highway system? 
Your views do fit somewhat neatly into libertarianism from what I've seen, which used to be a tentpole for the Republicans but have increasingly been splitting off into their own groups (eg, Ron Paul). Libertarianism always seems to fail to account for the fact that private industry has effects that are not accounted for by a free market, and that government is needed as a regulator and to enable innovation. 
In terms of Social Security, it makes it so that small employers don't have to go off on their own to provide pension plans, though obviously they should. Similar arguments have been made about health care - the lack of a government system has prevented investment in the US because it's too costly to insure in the US's fairly regionally monopolistic markets. 
Yes, the lack of a cost of living adjustment is going to suck for those on it. Luckily inflation has been low to nil and the cost of living is relatively flat with last year because the energy markets collapsed. 
In terms of the tribe example, you ignore a perfectly valid third possibility, that the 10% of tribe that's hunting has freed up the capacity of the other 90% to do something else useful. They could be making tools, engaged in agriculture or childcare, or inventing improvements to existing stone-age technology (Flint Axe, now chipped with Granite Rock for extra sharpness when spear stick hard). Overall, people tend to be productive. A small, small minority isn't, but the vast majority is, and that's who you plan for. Just because they're not hunting doesn't mean they're not being useful. Without hunters and meat being able to free up the time and resources for a lot of the rest of the tribe human civilization wouldn't have happened. 
The government derives its right to your useful output via the general welfare clause and several others in the constitution, including the 16th Amendment. I don't have the right to your output, but collectively we all derive various protections and benefits from the federal government that wouldn't be possible without income taxes. Civil society wouldn't work well without them, which is why you see countries with weak federal systems failing or being overrun by parochial interests (not that ours doesn't suffer from the same ailments).
As I said previously, I did not bring up the subject of taxes, as people already have their minds made up.  Keep Social Security, I don't care.  Hell, let me pay in 3/4 of what I am now and I'll opt out.  I'll do better with the 25% than the government will with 75%.  But don't count solely on it.  Put forth some effort on your own.  
Take some responsibility for your own existence.  We 10% have broad shoulders, but eventually there is more than we can carry.
Saying that taxes shouldn't be brought up in a discussion of Social Security is like saying that Space Shuttles and Rockets shouldn't be brought up in a discussion of interstellar travel. The point of Social Security, like Russell said, is that it's a safety net when all else fails. Bad things happen. People invest all their money with Bernie Madoff and go from a comfortable existence to nothing. Large medical bills pile up and wipe out savings. 
You can already opt out of Social Security by returning any checks you get from the government once you get that old. However, the point of a safety net is that it's there when everything goes wahooni-shaped, so you can't opt out of paying the taxes because 20-30 years down the road you might find yourself in dire need of it. It's an insurance policy as much as a pension system, and it's there when private savings run out because you've lived longer than you budgeted for.   
 Russel, I don't really mind paying some taxes.  It's when it gets close to, or over, 50% that I really get angry.  I help people voluntarlily all the time. 
Which is why donations made to various groups are tax-exempt, to encourage that kind of behavior. I don't think there's a tax bracket in the US right now that is 50%, but historically they've gone higher than that and the country hasn't collapsed.