Here's the thing about why Raimi handled Venom like he did: Venom is, at heart, a petty, envious loser who, when given the chance to have power, goes around blaming all his problems on another, seeking vengeance, and randomly killing and eating people. He is, by all rights, *not an anti-hero in the slightest*.
Raimi understood that. He also understood that the fans demanding Venom were demanding the anti-hero, because of shallow 90s kewl. I can entirely understand why he was pissed about it being forced upon him. This is why he gave the fans what they wanted ( Venom ), and pissed them off anyway ( because he didn't feed their 90s kewl indulgence ).
Raimi never cared to for Venom, because the character was so convoluted, because of the many hollow adaptions(the shallow 90's kewl, as you said it), that really didn't possess any real concrete foundation, to the character, that he felt, he could really fashion or build any credence around. He stated something similar, on many occasions, when speaking about his disagreement with Avi Arad about been forced to include the character in Spider-Man 3.
The thing is Brock originally, was an envious person, who felt slighted, powerless to change his misfortunes, and blame many people & society in general, for personal problem he faced in the world. That much has always been true. However, the change came when Brock posses the Symbiote, and became Venom...."Originally", he was a ruthless killer that devoured/consumed those he seek vengeance against....against "ALL" he felt slighted him, contributed to his misfortunes, and those that stood against him in some 'form or fashion' or stood in his way.
This is the Venom most fans originally adored, and wanted to see how Peter/Spiderman, 'could & would' deal with such a deadly brute, whom has no remorse or concern for human life. Raimi said he could not do that(original) version of the character in the family oriented, kid friendly, style film he created, nor did he think that portrayal was suitable for any young person, going to see a film based on a comic.
So, I completely agree with you...that is not a mark of an anti-hero....far from it. It was when Marvel Comics decided to water down the tone of the character, and later re-established the character as this Anti-Hero, that can flirt with the fine line, of being a hero or villain, is when the character as a whole, became hollow and shallow shell of it's self, with no real substance...because his main focus became just Peter/Spiderman for a time, and the Symbiote, was able to leap from person 2 person...taking on many different personalities & justifying it's ideology, depending on the personality in possession at the time.
Neverless, by that time, fans had already thought the character was "kewl"...because of it's original portrayal. Not because of this anti hero bull; and, simply just continue to gravitate toward the character ever since, because of what had been established originally.