Devil's advocate time.
Ignoring the context and history of the argument in the thread title, which results in fan rage, etc, I have no issue with the structure of the argument ("you like X because of Y"), nor do I have any problem with someone making an argument with that structure. I actually dislike it when people think they know themselves better than others could, which can lead to scenarios like "I don't have a drinking problem!" when such is clearly the case based on all the evidence.
I think the argument itself, "You only like FFVII so much because it was your first RPG", does have some merit, but only in that there is a likelihood that a benchmark kind of bias might be created when playing something for the first time, to which you judge all other games that are similar. I can't quote studies or find them, so feel free to dismiss, but I'm certain I've read about such a bias.
Importantly though, while the argument may be able to be applied to some people, it can't be applied to all.