The band is only hated due to it's success, sad reality of metal.
I was having this conversation about a local thrash band on a board the other day...one poster stated that the band was so unoriginal because they sounded like a Pantera/Exodus ripoff, that they should just stop playing Thrash like the other shitty "nu-thrash" bands such as Municipal Waste....he then retorted to further posts that the only "true" thrash still going were bands like Toxic Holocaust and Warbringer...and I've seen both of them live and they're not very good, so I guess everyone has their own opinion.
I find myself still listening to the first 3 COB records most compared to the later material...again I think it's all the specific era or sound you get used to with a band...with Cannibal Corpse I'm used to Neil Kernon and Erik Rutan's production, as well as Corpsegrinders vocals...so it's harder to listen to Barnes and lower valued recordings. Exodus is another band whom I listen to Tempo of the Damned through the reissue of Bonded by Blood and Another Lesson in Violejnce rather than the first 3...either way it's all subjective and I guess you're just going to have to deal with it.
I think what's causing this also is the fact that COB shirts are being sold en masse at hot topic and mall t-shirt kiosks. I work at a guitar store and I've seen kids as young as 10 come in with Hatecrew Deathroll shirts on, and when I say "nice shirt dude, great album" they give me confused looks...this one kid even said "I just bought it cause I liked the design, I thought it was for a horror movie." When most "metal" fans hear that they'd want to punch said kid in the face...hence the hate. I believe sadly they've drifted into the "trendy" metal wave...alongside Trivium and Bullet For My Valentine.