1. He let Vegeta go, knowing that the guy could be a great danger, even Krillin told him that he is a great danger, even so Goku considered that he could defeat him later.
2. He gave energy to Freeza, which allowed him to return as a Freeza wick and if it weren't for Trunks, everyone would go to shit (not to literal hell)
3. everything that was the final part of his fight with Cell, yes, he stopped Cell from destroying the earth, but he was also the one who gave him a seed from the hermit and sent Gohan to fight, even though, for What did he do? To let his son fight Cell and recover to his full potential???
4. Majin Buu, he could have defeated him, even if he had a time limit, he had ENOUGH time to defeat him, but no, he passed the responsability to goten and trunks...and we know how that ended up at the end.
5. the final part, Moro merged with the earth