I tried 3 times to check out your link and each time my computer locked up. So your source sucks in that respect. I didn't get enough information to determine their claim was credible, so the jury is still out on that one.
The only thing I could see was that they are basing their estimation on a picture. So if you don't consider the fire dept. a credible source for estimating crowd volume, we can come up with our own estimates using their logic...
The Tea Party/9.12 rally in Washington 2009:
You are claiming that is 1.2 million people?
To put this in perspective, this is what 500,000 people look like...
And the tea bag crowd doesn't look bigger than that.
And just for fun, let's compare the tea bag numbers with
a legitimate protest rally that drew a minimum of 400,000 people...
Anti-war rally in Washington 2005:
Not only does this rally take up the same space as the tea baggers,
it also fills up all the adjoining streets from blocks away.
And you're claiming the tea baggers out-numbered them 2 to 1?
That doesn't pan out in those pictures, which is what your link
used as a measuring stick.
I won't even get into the issue of what was the reason for both groups being there in the first place. The anti-war crowd marched on Washington 2 years after the illegal war had started, which was long enough for people to see what it was costing us in dollars, lives and our reputation around the world. It makes sense when the government gives up that much, on someone else's country, with nothing of equal value in return, that a certain segment of this country's population, would get mad enough to march on Washington. The only other time we've seen a crowd of that size have a rally there, was the civil rights march that culminated in MLK's "I have a dream" speech.
These tea baggers marched on Washington less than 6 months after a new President was sworn in. You can't possibly do anything in that amount of time that would make a march such as this necessary. But it does explain all the empty, emotional rhetoric tea baggers say when you ask what are they protesting.
"Obama's like Hitler, dude!"
"Don't tread on me man!"
"Next time I'll be armed"
"I'm no Oswald! He didn't have a Glock!"
"I'm protesting the raising of taxes"
(even though taxes have technically not been raised)
"Obama's a socialist! He's trying to take over.........uh..........um...........stuff!"
"And don't tread on me, man! Did I already say that? Well, it's worth saying twice. I like that one. So keep your treads to yourself. Especially, if you're Firestone. Those treads kill people"
BTW, this was the pro-war rally in 2005 that same day in Washington, which got the same amount of news time the anti-war rally got from all the alleged, mythical liberal media (85 seconds). Which is strange, because when you compare photo's, they don't look equal as far as an event is concerned.
Pro-war rally in Washington 2005: