Once he starts remembering specifics about his regrets he'll certainly appreciate it, but yeah; it's my personal canon that he's very much the sort of 'let's focus on the good you can do instead of the bad you've done' in most cases. (Even himself, to a degree.) Yay redirecting negative energies!

...besides, so long as Phineas isn't actively trying to hurt anyone, he'll forgive a lot.