We can discuss the principle of investing the Social Security tax in the market, the financial solvency of the system as it stands, and countless other parts of the issue. What shouldn't be done is to imply that benefits will be cut when no such thing has been proposed because it is outright misleading to do so.
The principle is worthless without the details. It is no great stretch of the imagination that when Bush talks about SS privatization he is thinking of the proposals from the commission his administration put together. It is fair and honest to look to those as a "guideline" until Mr Bush or the Republicans in Congress provide something different. To deny this is bullheaded at best.
If you only want to discuss the "general concept" of investing SS in the market then you must own up to the fact that you are allowing people to gamble with money which is specifically set aside as a safety net for them. You must admit that some run the risk of losing all of their SS.
Cutting the rate of growth to inflation from wages or just straight up, it is still a cut. A reduction in potential buying power, plain and simple. Indexed off wages you have more, off inflation you have less. Especially when you consider that inflation is an index which is determined based on a govt-determined set of goods and can easily be manipulated.
Just because you label something a lie doesn't make it so. If anything you are being intellectually dishonest regarding what is being proposed.