I find it interesting that you do this. I think that the title is a part of the original work. After all the author did put energy into selecting the title, just as he selected the words to use for the content of the article. I suppose the person that submits the link might not be the author, which is probably what happens the most. I'm still torn.
Respect for the original content is a high value at Hacker News, but so is intellectual substance. These two values sometimes conflict, especially when it comes to titles. When they do, intellectual substance wins.
It has to. Otherwise threads would get sucked into the black hole of arguing about titles. In that world we would probably be wading through angry denunciations and counter-denunciations of this one, for example, instead of pure HN gold like https://news.ycombinator.com/item?id=9025587.