For editing that's why every post or every reply have " quote " option. You can use simply if you think there is possibility some thing wrong. If you queted than OP will not able to edit or delete your quote.
Quote can't be an evidence as well, because any user can falsify it.
Here should be delete option. Sometimes some comment become useless. So OP can delete if he think it's not necessary now. Some one bumping thread , he should delete previous bump before next bump after 24 hour's.
Why delete post instead of edit it and showing when it has been edited?