Some people seem to love to cash in on BZ stabbing Madara. I may too for jokes, but some seem serious about it. I will explain why BZ was able to get Madara.
1) BZ was in control of Obito's body, without that he wouldn't of stood a chance in hell at piercing Madara
2) Madara thought that BZ was his will, thus would simply ignore his presence regardless.
3) Madara does not have negative emotion sensing, and as such wouldn't be alarmed because BZ was "his will" after all.
These are the reasons -PLOT- why BZ was so easily able to betray Madara.
:bye: