A simple analogy:
Just like gay marriage violates the sanctity of marriage, LFR violates the "sanctity" of raiding. It's that simple.
Every culture throughout all of recorded history has regarded the family unit as the foundation of their society. This has always been based upon a male and female in some sanctioned union (marriage). Society is dependent upon the family unit (marriage between a male and female) because this is the future generation of society. If the family unit is strong, then the society will have a strong future. For this reason, society has honored and protected marriage, imbuing it with certain privileges.
This also applies to WoW: Family unit = Guilds. Guilds are the foundation of WoW's society. Raiding is dependent upon the family unit. If the family unit is strong, then raiding will have a strong future. For this reason, the players have honored and protected raiding, imbuing it with certain privileges.
LFR devalue the very concept of raiding and family (Guilds.) Gay marriages devalue the very concept of marriage. It's that simple really. Matter of right vs. wrong. There's no middle ground. It's also a matter of morality.
TLDR: LFR is ruining raiding just like gay marriage will ruin marriage.
Casuals are seeking a special right just like homosexuals are seeking a special right. Homosexuals already have the same right to marry the rest of us have-the right to marry a person of the opposite sex. Casuals already have the same right to raid the rest of us have. Limiting marriage to one man and one woman doesn't discriminate on the basis of sex or sexual orientation. Limiting raiding to real raiders doesn't discriminate on the basis of casual playing.
Infracted: Trolling [ML]