why would gold d roger ask garp to take care of his kid instead of asking rayleigh?
logic
Garp: marine
rayleigh: first and probably best mate
Roger wanted Ace to live a life without piracy and without anyone knowing him being born to the pirate king. Him and Garp obviously had a bond and he could pretty much see through him. Just like how we know that Smoker wouldn't actually kill Luffy. Roger knew that Garp wouldn't just toss Ace away.
If i had a son and didn't want him to be known as my son or as a pirate i would rather give him to a marine that i can trust instead of a pirate/ex-pirate.
how come rayleigh didn't go to save ace on the war, come on the son of his captain??
It wasn't his battle. He's a pirate and knows what the life of a pirate is like. Ace isn't Rayleigh's nakama and Rayleigh has no emotional attachments to him. Ace was a Whitebeard pirate and as a Whitebeard pirate it was his crews task to save him. Knowing all this why would Rayleigh save Ace? not really his job.
Even Zoro wouldn't go there to save Ace. Unless Luffy directly asked him to come with him he wouldn't do it. He has no obligation to do so.
If Marco was the one who was captured by the marines Luffy wouldn't go.
and how comes shanks didn't know that ace is the son of his captain
Roger never told anyone. He didn't want Ace to be affiliated with pirates in any way. Not to mention the fact that Ace told Shanks he was Luffy's older brother would further confuse him.
and lastly you think that roger is an idiot like luffy?
Yeah, i do.