Why is everyone so convinced the prophecy is correct?

[ratalman]

No: HPFGUIDX 82279

Kneasy wrote:
If he knew that the prophecy had been partly overheard, he must
do something to protect them. If he read the prophecy the way I 
have he would not be so punctilious. He couldn't even fulfill that 
role; in his wisdom he passed it over to an agent of the enemy. If 
DD had been serious about the Potters having protection, the 
secret keeper would have been a trusted Auror or even himself.
And what protection did they have?  A renowned hot-head, 
unreliable and of no real use if Voldy turned up, except as a 
pointless sacrifice. 

Robyn:
But we learn in PoA that Dumbledore wanted the Potters to use 
him as their secret keeper, as he was worried that information 
about them was being leaked to LV.  The Potters refused, 
preferring to use Sirius, on the grounds that Sirius would rather 
die than betray them.  That does beg the question, however, why 
the Potters would refuse the services of DD: did they have some 
reason to suspect his intentions, or, maybe they didn't take the 
threats seriously enough?