If afterwards he says he shouldn't have been there and done that

He says it was an 'excellent experience'. He considered the 'experience' to be good enough to sign up several more times, including as a mercenary, and to then brag about it.

is anti Israel

Well, he isn't. He's even friends with zionists.

and his opponents are pro Israel and in the case of Susan Collins literally voted to send his ass and all the other thousands of troops there

She didn't force him to sign up even once, let alone several times.
He also isn't any better in terms of policies - he wants to strengthen the military.

My reaction is he wasn't killing civilians for his own kicks

He has literally said that he had fun doing it and bragged about it.