The earlier you plan to retire the less SS matters. If you retire at 30 like MM you already need to fund a 30-year-plus retirement without SS. Factoring in SS for 30 years from now won't help you much. Also, SS's future looks less certain if you're decades out. If you're ten years away from SS, it probably will look like it does now, so go ahead and figure it in. In-between is tricky. They could raise contributions, which would mean you could still rely on it. They could raise the retirement age; they could add more means-testing; increase the minimum amount of credits you need to collect; or they could cut the payout.
SS isn't going away completely. Adding the payroll tax, so people see the SS contribution on their paycheck is political genius. But the idea of a fully-funded trust fund isn't quite right either. It's an accounting fiction full of IOU's from the general treasury. Of course, there will be ongoing revenue from whatever generation is working at the time, and there's no reason SS can't be run on a deficit like the rest of the government. It could be partially financed out of the general treasury from those IOUs, and that will either increase the government deficit or income taxes will need to be raised.
Like global warming, it's a problem hard to solve politically. The consequences are further off than the next election cycle, and any solution will be costly. The longer we wait, the more expensive it will be.