I'm not fully sure about the reason that made you get -8 Karma but I think I have somewhat idea about it. You might be one of those guys that Sheriff reported and if that's the case then I recommend you to make good posts so you may get better Karma.
I don't really have anything with you because I'm basically here to drop my prediction about the Man United and I believe that in the coming match they'll perform better. Brentford isn't a tough competition for them and that's why I believe they will win the match of tomorrow.
If we check the recent matches of the Brenford then we get an idea that how poorly they have been performing in their recent matches and if they continue performing like that then they won't be able to win any matches against good clubs.