Harry has shown again and again that he can't lose, and instead doubles-down. He did so with Hermione, and now Lucius has killed her. If people realise it's Lucius, all the better for him; nothing can be proved, but he shows himself to be extremely dangerous and willing to protect his family.
All the better for him? You just told us why it is bad for him. Harry can't lose and instead doubles down. His accomplishments so far despite being about 10 years old and newly exposed to the wizarding world indicate that given time he will be a threat or at least a significant potential nuisance to Lucius in the future. If Harry knows that Lucius killed Hermione but cannot prove it basically Lucius is going to need to have Harry killed at some point in the future or have his life (and vulnerable resources) at risk for as long as Harry lives. This is not a desirable outcome.
The reputation influence and aura of fear that you allude to would perhaps have made it useful to have Harry killed. Having Hermione outraged but unable to prove anything (may be) a minimal risk and would make Lucius seem more impressive. But Lucius is enough of a strategic thinker that he ought to know that creating a Harry with Nothing (or at least significantly less) To Lose and with a grudge against him isn't worthwhile. If he is going to use violence against that which Harry cares about he essentially needs to use violence to kill Harry of outright. If not then three years later he might find himself obliterated in his sleep by a satellite that has been pulled out of orbit and directed at his house.
Harry already said "if you do this thing, Lucius, I will take you for my enemy". And that didn't stop Lucius, and so presumably he believes Harry has already taken him for an enemy anyway. The thing to do with an enemy is attack them.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 88-89. The previous thread has passed 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: