Believe me Licorice isn't and probably hasn't been an ingredient in Guinness. There were some very strange beer additives used in the early days of the history of commercial brewing, stuff like Arsenic. Laws in the UK and Ireland were established banning a whole slather of additives, including most herbs and spices (exceptions were made for most Gruit ingredients (no Licorice isn't one))
This started big time in the 17th century, (before Guinness) and by the time Guinness came along brewers were trying very hard to prove the "healthfulness" of their beer the "Guinness is Good for You" motto comes from this period.
If you want to put Licorice in your beer fine, do it (probably everyone does it once - I did) just don't try to support the decision with spurious crap.
Adding Licorice is a 1960-70's home brew idea, dates from when home brewing was illegal and you couldn't get stuff like roast barley, base malt, hops, decent yeast, and a lot of other ingredients that help make home brew palatable.
Imagine having to brew with LME, stale POR or hop oils, white sugar and baking yeast... Thanks Gough for legalising home brew.
Mark