Or, save yourself the trouble and smoke, or vaporize, the MJ and drink the beer.
100% agree.
Beer will never replace hops either. Hops add 3 elements to beer. Bitterness, Flavor, and Aroma. Flavor and Aroma are the only components that weed could replace, as it does not have a high alpha acid content (im about 90% sure this is correct).
So really there would only be two reasons to add pot to a brew
1). THC.
THC can only be extracted using certain solvents and some types of fats. Butter is the most common for extracting thc from the bud. This is why brownies as well as other baked goods so popular among the cannabis community. If your not going the baked goods route the only other option you have is to use some sort of solvent (alcohol with 25-30% abv or higher, everclear, isopropyl alcohol, or food grade glycerin - what i would use if i were to put thc in my brew). cannabis is soaked in the solvent for days to weeks being shaken daily to extract the most amount of thc, the weed is strained from the liquid, then the solvent is allowed to evaporate leaving behind a sticky tintcure with highly concentrated thc. this could be added anytime after the boil(as it will evaporate with steam).
All of this aside, adding pure thc would not add anything to the quality, flavor, aroma, body, head, or bitterness of the beer, and if anything could add off flavors to your brew. There is also the school of thought that the more inebriated you are, the less you can enjoy the subtle characteristics of good beer.
2). Flavor
Regardless of quality, the raw taste of cannabis to me is not good(imho). Maybe it could work with a double or fruit IPA, but that could be a stretch. If there is interest here, i see it being sparse at best and for most brewers ending up being a weekend project not to be repeated.
Getting drunk is not the reason most homebrewers brew, so adding another mind altering agent doesnt really make sense. If you like the taste of raw weed then by all means give it a whirl, but I'm willing to bet you wont try it more than once.
-My 2 cents.