I have always helped boaters in trouble. Last summer a guy on a PWC pulled up to us as we were anchored and told us a family of 6 was stranded on the lake, they blew their out drive and needed a tow. We scrambled to pull up anchor and off to rescue we went. We towed them to the ramp and helped get it loaded.
I just hope others will rescue me if I get in that position.
As satisfactionII said "Do unto others = good karma".
Besides, it's also a federal law if you know of a boat in trouble you must render aid. If your boat is not capable of helping then you must stand by till someone who can help comes.