There's a lot of guff on this thread. Here is my two cents worth -
1. The opinion has been stated that indicators must be worthless because you can get them for free; why would anyone let you know what they were for free if they worked? I suggest you read "Way of the Turtle" by Curtis Faith. In it, he details how a class of 20 students were taught a precise way to trade, which was unambiguous and unequivocal. When let loose in the markets, only 20-50 pct of these students actually followed the very clear rules given them, which would have made them a fortune. In other words, you could tell 1,000 people a profitable trading strategy for free and the majority would just ignore it anyway.
2. How can you possibly know the value of an indicator without determining your exit strategy beforehand? Most trades will be in the money at some point and out of the money at another - how you get out of the trade determines the value of the indicator. In "Trade your way to Financial Freedom", Van Tharp details how a random entry system can make money, using suitable exit criteria.. these revolve more around money management than anything else.
I find entry a small part of the trade - knowing what to do if the trade starts to move in your favour is more challenging.. trailing stop loss? targeted profit point? combination of the two? For this reason, I believe it's impossible to "prove" indicators are worthless, any more than any statistic is worthless (e.g. GDP growth last year was +3pct, now it's -1pct - is GDP as a figure worthless??)