Because they will ultimately go nowhere and eventually turn into flame wars with "my favorite character is more Mary Sue than your favorite character" as the premise? :D
My belief is:
1. Spell Card rules
2. Break them and Reimu will probably die inadvertently
3. ???
4. GENSOKYO IS DESTROYED
Sometime this summer, I turned into a CANON IS GOD, PRIMARIES ONLY, SECONDARIES SUCK fag, so I have trouble enjoying Touhou these days. orz