I talked to the HLL early in the game and as of yet haven't found any other use for them (if talking to them early in the game was useful at all LOL) Anyway, I ripped off the Mook and the HLL still show up in green, my rating with the Higardi is still friendly and as of yet, I've seen no trouble for my efforts.
If there is any trick to it, it is just to stay away from the HLL, you know "lay low for a bit"...if there are any negative effects, I have yet to see them...so that doesn't mean I won't, but I could kick their Elvis-look-alike butts on any Sunday.
I haven't seen anyone say yet that taking the thing got them into any trouble.