Freechoice said:
Council doesn't believe you in ME1? Ok, racist assholes. Council still doesn't believe you in ME2 even after beating Saren and/or installing the human council? Bullshit. Basically everyone that wasn't on the Normandy or isn't Martin Sheen doesn't believe you about the Reapers even after killing one and having real fucking evidence about it? Fuck it.
´
If you understood basic politics or government managment you could see why they chose to deny it.
If you feel like it:
http://www.youtube.com/watch?v=cZplcAuAAEI
TL;DW? (Too long, didn't watch?)
First point, compare a Geth Dropship or Mothership with Sovereign. They do look similar, don't they? Not only that, but during an intense spacefight we don't really notice details.
Not only that, but it is stated that Sovereign exploded in a lot of parts, most of them being taken by the keepers in some sort of cleaning process.
And those are just the physical arguments. The Council doesn't want to admit that it was a Reaper leading the Army because:
a)they have np hard evidence of what happend. Vigil powered down after spending the last energy of the base activating the conduit. The message on the first colony attacked overloaded.
b)The only Reaper present in the attack was destroyed and no one was exactly worried about taking pics, when he was destroying entire fleets. After some (little) time passed, they didn't even had the pieces of Sovereign thanks to the keepers, and they have no knowledge about Reaper technology. It could be easily argued that the Geth just created a Dreadnought.
c)They didn't want to incite fear on people. After 1 or 2 months, and given the circunstances above, they had no recording of the attack, no evidence of the Dreadnought's origins. They had no reason to believe that the Reapers existed. Considering this scenario, and if you were a Councilor, what would you make official: That the Geth, that they suppressed and fought after the Battle, are now beaten and there's not a remote chance of another attack, or that mechanical monsters old and advanced as fuck were coming to get them?
If I was on their position, I can't say I would do things differently.
P.S: The turian councilor is still a dick, though.