1. FFVII and FFVIII are very different from the previous games. In the eyes of someone that really likes the older ones, they aren't even the same series. They wouldn't like seeing those games compared to theirs.
2. They are mostly that way due to experiences with the FFVII diehards mentioned before.
3. There is seriously no "true fan" though as it is all subjective.
1. That's the whole point this certain fans doesn't like their precious older or mainly FF VI being compared to FF VII. Like I said it's like poison for them. I have seen a lot of these guys attacking a poster that post "FF VII is the best FF". You'll see a barrage of posters attacking FF VII and the guy.
As for it isn't the same series. Please the only difference is, FF VII and FFVIII are just in 3D but it still plays the same. Random battles, ATB system, the battle menu consist of Attack, Magic, Summon and Items.
2. With my experience. I haven't seen any FF VII guys hating on any other FF besideds FF VII.
3. I think you misunderstood me. A true fan never hates but gives constructive criticism. I liked FF XIII but I still critized it.