arjun didn't want to he did on request of krishna in the presence of krishna furthermore arjun's curse did come true when pre-vastraharan when karn badmouthed draupadi he curse karn that he will loose all knowledge and atma se darinda hoke maroge so yup his curse came true(based on Star Bharat)
karna did forget his skills and knowledge than krishna made him realise his sins furthermore karn volunteer to be killed after he realise his sins
in whole MB krishna played lots of chal to win the war to name a few jaydrath death when he use his sudashan chakra to block the sun and karn vadh to kill him when karn is weaponless...its all due to krishna
he hails as a great warrior that he was no doubt on that but the man is too arrogant and has no respect for womens
This is actually StarBharat. In the epic even after getting down he was not weaponless.
He was just killing time. All his weapons had been neutralised by then. He was completely wounded and hardly had much survival chance anyway (someone has given in the citation in the forum. It might be in the first page itself) Karna had anyway lost, even after getting down he tried to use Brahmastra.
Yes Krishnaji did ask for Arjun to attack but because he knew that Karna is killing time and that was useless
Plus he had three curses-- Parashuram (to forget Brahmastra right at the time) Bhoomi Devi and a Brahmin
Arjun ka there wasn't any curse