Even before the “Sandcastles in the Sand” episode of How I Met Your Mother, the should or shouldn’t Robin and Barney issue has been debated. Since the last moments of the episode (s.i.t.s.), it had become an even more prevalent issue. (Examples of the discussion: howimetyourblog, HIMYM Message Board…).
I don’t want to spend a ton of time talking about the consequences, affects, etc… for that there is a great discussion going on here concerning the next few episodes. However, I feel that Barney made the best case for Barney and Robin back in Season 1, in the episode entitled Zip,Zip,Zip. If you need to visualize it in a more current setting simply imagine Barney says “Stella” instead of “Victoria.” Enjoy.