dreams

my experiences are universal and provide an undeniable framework for understanding all of reality

Why would Snape think this...? He was SO ANGRY with him in PoA. He thought Sirius not only tried to get him killed as a teenager - but was the final straw in getting Lily murdered. He wasn't having anything of the 'Peter is alive' bullshit, that was desperate, manipulative lies by two sneaky murdering bastards trying to get trust and access to kids.

I also love the implication that general people would absolutely believe Peter would betray the Potters??

Peter, who joined the Order and stood by them even though he isn't nearly as capable. He followed them through thick and thin. Even Sirius didn't think he would betray them!

Sirius, meanwhile, has a history of breaking rules, violent acts and mischief, being sneaky - and has family associations with Voldemort.

Sirius SEEMED very loyal, but... someone leaked the Potters location, and Sirius was the last known person discussed to be secret keeper.

Dumbledore gave evidence - but as Sirius' 'employer'... what could he possibly say?? 'Sirius was the last person James discussed as being Secret Keeper. I offered myself, but they refused.' - He doesn't know anything else!

What use would 'I am certain the Sirius Black I thought I knew wouldn't have betrayed them' in the face of two dead Potters, a severed finger from an exploded wizard, a dozen dead muggles, many unbiased witnesses - and a Sirius Black who laughed at the carnage??

''(even though Harry would have been just as safe with Sirius)''

He would not have been just as safe in a Wizarding home.

Petunia changed her mind on kicking Harry out in OotP because it would have put her family in further danger. When Harry turned 17 and the charm broke naturally - they had to go into hiding because the magic wouldn't protect them anymore. Voldemort himself had to wait for Harry to turn 17 to try and hunt him when he changed locations.