Everything the gov't does is done inefficiently, especially compared to how efficiently it could be done by the private sector. Not only the direct costs, but the indirect costs like payment of fraudulent claims (which is rampant), and lack of means-testing. How is it economically efficient to distribute monies to those who don't need to spend them? It isn't, and yet it happens all the time with SS. And don't even get me started on the SS disability benefits.
I don't think that anybody is arguing for the "privatization of gov't", which is probably an oxymoron. But due to both increasing gov't costs and inability of gov't to keep up with the times, the way gov't delivers services increasingly follows the model of the gov't as administrator and overseer, and private contractors actually delivering the goods and services at the ground level. This is especially noticeable where anything actually has to get built, like defense and infrastructure, but is increasingly the case at all levels of gov't. The unions of course are scrambling to bring more jobs directly into the gov't, and that provides the tension that can only be relieved by the busting of the public sector unions.
"Cut SS and Medicare to finance tax cuts" is a red herring. You NEVER "finance tax cuts"; taxes are what finance all programs, not the other way around. You begin with the social programs in a position of primacy, but that's not the case: taxation necessarily comes first, THEN the social programs. "Cutting spending" never finances anything--all it is is a decrease in the financing level of that which is cut.
Have you worked in gov't? There is no credible way to claim that SS and Medicare cannot be made more efficient. Or ANY gov't program,. for that matter. They only question is how, what the time frame will be, and whether or not it can realistically be politically achieved.
This whole argument between trickle-down and trickle-up is unhelpfully polarized, as well. I don't see why it cannot be a combination of both mechanisms. One cannot, does not, and never has, existed without the other. It's not a value judgment, just a fact. I think that anybody preaching the dominance of any one of the two mechanisms is barking up the wrong tree, and does so out of a political or moral motivation, not an economic one.
Don't give the wealthy SS benefits? Absolutely agree, we need means-testing.
Scrap FICA and replace it with VAT? Absolutely agree.
Single-payer health care? Disagree, I have lived in countries that have it, and it doesn't work as well as the US used to, before the ACA. It's a great and noble idea, but in practice it just doesn't work like in theory.
Don't have inflation? I'm not sure how you would even approach this, given the fractional reserve lending system, which at this point is bedrock. Do you have a proposal?