I think that there should be a "Delete Comment" option for ONLY the the person who created the comment on the thread. Or the creator of the thread.

Like when you double-post its annoying that you can't delete it. Only make it something else. Or if theres a comment that's spam the thread maker could delete it. 

Post your opinion ^^ 

 I'm a bit torn on this but it's no support in the end. :/

It would be realy confusing if someone went back to a topic and just deleted all posts of his. Or the topic maker delete post that simply does not fit with his opinion. :c You/They are not mods, shoudn't have thoose powers.
It's possible with "edit" already to... "hide evidience" but at least you still see that one posted at all.

You still can edit out the text of your double posts. It's not gone then but not as "prominent" as before. Totally sufficient in my eyes. ^^  

Copy and paste the evidence ;) 

 -copies last post for example-

Hope you don't mind me copying your comment Yaizhbeen 

I don't mind it at all, feel free to copy my comments :). After all, I understand that it is a global need to preserve my wise words for the next generations :D.

-.- I didn't say that XDDDD