Well, the vast majority of people - black, white or whatever - love Eminem. He's ONE OF the greatest rappers of all time, according to pretty much every rap fan, critic or rapper.
The people who try to discredit Eminem are mainly just loser trolls on message boards. Let's take a look at their shytty arguments:
1) They like to call Eminem "corny", and cherrypick random songs like We Made You or Fack or whatever...ignoring the fact that you could do that with literally every other rapper. Nas made Nastradamus. Jay-Z made Anything, Hollywood, I Know What Girls Like. Rakim just put out a coaster. KRS-One has all kinds of shytty songs. Ice Cube has enough shytty cornball songs post-War and Peace to fill at riple album. Every other rapper put out cheesy singles and wack material and gets a pass, but with Eminem, it's all they can focus on, and it's stupid.
2) They say Eminem's "discography doesn't measure up." SSLP, MMLP and TES are critically acclaimed, best-selling, and make pretty much every list of the best albums of their era, rap-wise, and including all genres of music. MMLP is called a classic by pretty much everyone, and SSLP and TES get that word thrown their direction as well. You have to live in a pretty dark cave to not think SSLP, MMLP and TES were great. And let's look at Em's other albums - only one of them was "bad." (Encore.) Relapse and Recovery got some mixed reviews on the message boards, I guess, but they both were received pretty well in every conceivable way - critical acclaim was positive, and they sold. People liked them. They're okay to good albums..both Nas and Jay have their fair share of those. But they get a pass, because they're black. Rakim has put out as many meh albums as good ones, but he gets a pass. KRS-One, LL, Ice Cube, all have made as much wack shyt as classic shyt. But they get a pass.
3) They try to claim Eminem is a racist, for the Benzino thing, and this is really their whole motivation. They have some pretty massive racial hangups for whatever reason, and just cannot, CANNOT, forgive Eminem for saying some racist lines on a basement song when he was 20. These same people post unbelievable racist shyt in their posts on a daily basis. They also love throw around f-ggot and hate on gay people like they're auditioning for Westboro Baptist Church. They also ignore the fact that every human being says something racist at some point in their life. Eminem apologized like a million times for it, in written form, on camera, on record, and nothing is good enough for these people. 50 years from now, they'll be sitting in rocking chairs on the porch, grinding their teeth about what Eminem said. For the rest of their life, they'll never let what Eminem said go, but they'll turn a blind eye to every other person saying hateful shyt.
The trolls that shyt on Eminem on message boards might be loud, but they are not many, and their shytty arguments don't really matter. Nobody cares. Almost all of your favorite rappers love Eminem, and that is a fact. He singlehandedly made being a white solo MC acceptable.
(Note: I don't think Em is the GOAT, but he's in consideration.)