Being a Social Democrat means you want Capitalism with Social Safety Nets. Wanting change via reform is called Reformism, not Social Democracy. You can be a Reformist Democratic Socialist.
Secondly, you really need to revisit history. American democracy is not a marketplace of ideas, but lobbyists and money. The parties in power are those that can fundraise the best, and they do so via capitulating to the wealthiest. The only trend against this comes from outside pressure.
Again, your stance on electoralism is unfounded and immaterial. Yes, voting is good, no, you will not get the change you want past FPTP by voting for it.
You again are completely butchering what Socialism and Social Democracy mean. Social Programs are government programs, they are a part of almost all systems. They are not synonymous with Socialism. Social Democracies are Capitalist states with large safety nets, otherwise they would be Socialist Democracies.
You did not point out a flaw with Marxism, you pointed out a flaw in your understanding of Marxism.
For the last time, the material conditions are NOT THERE in the US for a Socialist Revolution, as long as the US retains it's status as an Imperialist state that props up higher standards of living off the backs of the third world. That is why republicans exist, Proletarians in the US are largely reactionary because they benefit from the status quo. The US is a dying empire, and soon there will be the material conditions for a Socialist Revolution, but fascism is also the violent outcome of Capitalism in decline. You have not once addressed any of this.
I have not done any Ad Hominem attacks, I have not misrepresented your arguments. I have attempted to fix your misconceptions of Marxism, Social Democracy, and Socialism in general, none of which constitutes misrepresentation or ad hominem.