It's not just the bright sunshine and Brazilian colours that mean there are no shades of grey at the forum. Much of the politics is in black and white
When it comes to the Iraq war, a straw poll - and the posters and graffiti all around - speak with one voice: "farce", "imperialist ploy" and "long live the heroic iraqi resistance".
No space, so far at least, for nuance or any sense that some good may come out of the Iraqi election, however tragic or compromised the circumstances. For a range of views - by no means all pro-election, but much more thoughtful - see Iraqis on openDemocracy.
Similarly, the word is that Lula, the Brazilian president, may get a pretty rough ride when he comes to an early morning event tomorrow in stadium. The majority here clearly think he's gone too far in making deals with what is known here as the neo-liberal order.
Before the week is out Hugo Chavez, the president of Venezuela, is almost sure to be greeted as man of the forum. Not too long after Lula flies off to Davos tomorrow afternoon to build a bridge to the suits, Chavez jets in to Porto Alegre to express solidarity with the T shirts of the MST (Brazil's Movement of Landless Workers).
Chavez comes fresh from overseeing occupation of land in Venezuela owned by an English Lord. The man has charisma and big cojones. It's hard not to chuckle at his recent offer of a one dollar bet to George W Bush that he would be longer in office than the US president.
But will Chavez outlast Lula? The countries are vastly different. Comparisons are not especially helpful.
This will not, however, stop the MST capitalising on Chavez's visit. They are shaping up for a big challenge to Lula a little later this year because they see the pace of land reform in Brazil as far too slow.
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