Not at all.
He thought Vic was misinformed.
His reaction is no more racist than Picard straightening Data out when he makes a mistake out of a lack of information and/or experience.
Picard didn't make it a point to not go near Data. He went
to Data, and
discussed the problem with him.
Sisko, on the other hand, did
not do the same with Vic.
Knowing Vic, I think he could be approached. I think he'd actually be glad to air out any concerns, given we know how much he cares that those around him are able to feel good about what they're experiencing.
Interestingly, in VOY's "Flesh and Blood," B'Elanna and Kejal end up having the discussion openly. Kejal was created with the appearance and some of the knowledge of a Cardassian, a species B'Elanna had a very, VERY bad firsthand history with. But Kejal made the point to B'Elanna that she's really an alien, and one that's made her own decisions and should be treated accordingly.
I think a Sisko-Vic conversation would go a lot better, though, and could have been very interesting because we'd find out a lot about how Vic sees himself.
I don't think it was a 'rant', and to be blunt, I get tired of this issue being brought up every now and then, usually by white guys, IMO, who really don't like the fact that Avery Brooks/Sisko was too 'uppity' (my word, not any that I've seen from an poster who had problems with this scene, but that's what I think is the problem some people really have with Brooks/Sisko's 'attitude' on this matter or others).
As others pointed out, it was Behr who wrote that; Brooks delivered the lines. How one feels about those lines should not reflect on Avery Brooks one way or the other.
As for my problem, apparently it's very much a minority one--it's simply that I think the writers did not fully consider the implications of Vic's sentience, and what it meant for Sisko to be indifferent to the plight of a living being.
Behr's objective--making it clear that the real 1960s weren't like that--could've been accomplished in many ways that would not have implied coldness towards the life of a rare alien. I think the conversation I suggest above would've been good. Or if not that, maybe even having Sisko say something like that he feels like he needs to hold his nose going into that holographic environment, but if that's what it takes to save this living AI, then so be it.
(And then follow it up with said discussion between Sisko and Vic. I think it would be VERY interesting if Vic knew the history and said he sees it as his purpose to do a far better job than his antecedents did. Perhaps--he is the embodiment of what people were dreaming of back then, when they dreamed of their world transformed.

)
He made a personal decision that had no impact on anyone but himself, and he changed that decision after talking to Kasidy.
Well, given that Vic's alive, another sentient being is at stake.