i think you should be allowed to like any game in the series, but not hate any of the games whatsoever. after all we're all castlevania fans in here and if we hate any one of them we're just going to risk harming the self-respect of the fans of these kinds of games and possible injure our respect for the series as a whole.
Well, if you mean collective hatred promoted by some people that stems from such concepts as "true Castlevania is only (2D, 3D e.t.c.)", then I am agree with you. Such behavior should be controled and not promoted as "official position of the True Old Hracore Fans Who knows Better", since it really harm fandom reputation and alienate newcomers who can have their own opinion, not based on the nostalgia and love for the old games.
However, thinking that people who a part of the fandom should unconditionally love all games in the series just because they are part of the franchise, no matter what their actual quality is, is wrong also. It is behavior that leads to the insane fanboism ("series is perfect as is, everyone who things otherwise are wrong / not fans / children e.t.c." mentality) and also obviously alienation of the newcomers. Besides, how could you deny what people opinion just like that?
Everyone have right to have their own opinion on any game in the series. And it is completely normal to dislike some of them, since not every single game in the franchise is perfect. Besides, we all have different tastes. Promoting "no hate for the games of the series because we are fans of this series" is like creating a censorship. It will shatter community even more so than any arguments about on what games should be.
I am sometimes come as person who intolerate other opinions, however it is not exactly like that. I admit that everyone have right to dislike some games in the series. However, the matter is how you put it. You can just say that in specific thread that you dislike that game for some reasons or you can repeat it like a broken record in every thread no matter what actual discussion is about. The second behaviour is what I was talking about earlier: it is essentially can create impression that this said opinion, not just opinion of several individuals, but opinion of the fandom as whole, and that is actually untrue.
So in the end, it is not matter of what you like or dislike, you can like or dislike whatever you want. It will not harm fandom and criticism can be much more useful than blind following. It is the matter of how you put it in words.