Gearing up alts does not help progression

I felt this topic deserved its own post.

I'm going to give my reasons why gearing up alts (while fun for those on their alts) does not help progression and can actually hurt it.

1) As soon as you bring one alt in you are immediately handicapped.
The alt while familiar with the fight, is probably not familiar with the fight on his alt.

2) Alts can potentially take gear away from mains who can swap specs for you.

3) An alt will require more support because they'll have less health, less hit, less everything.

4) In the end, when new content is released, mains drop their alts like a bad habit anyway.

5) If you have the chance to gear up and alt, you may not focus on gearing up your main to its fullest potential.

6) One person bringing an alt just makes 5 other people want to bring theirs. If you are handicapped by one alt, what are you by bringing 5?