So normal and heroic will fufill that challenge for "you", correct?Sure, it is better than nothing but it won't be available for 10 mans, so you group with 18 other people through LFR.
How high is the chance that some of them won't have a clue how to play? I'm sure that you would take the lead and yell at the baddies to get the raid done but how long until you get annoyed?
CC? Unlikely to last long. Kicking important spells? Please announce first, scramble to kick yourself, yell why no one is kicking. Raid mechanics? At least I had chicken.
That is of course the worst case and if CC/kicks/mechanics have a meaning.
Yes, there will be pleasant groups with dedicated players, but how many baddies got carried in the process which will then try to leech from normal mode guilds?
A harder game is more challenging. Overcoming that challenge is the fun. It requires that you improve your gameplay, that you fight for every boss kill.