Horrifying explanation for the Werewolf Incident
“Definitely not. Firstly, he was probably already being bullied - JKR has said that James and Sirius subjected him to “relentless bullying”, she implies continuity by having them still use an insulting name they gave him in first year, and the fact that Mooney’s is the first voice on the map to insult him suggests that Remus initially took part in the bullying, and did so in fifth year when that map was written, and when he was a prefect. If you are being attacked, and even the “policeman” who is mean to protect you is supporting your attackers, you have a right to try to protect yourself by getting something on them.
Secondly, it is unlikely that he was trying to get Remus specifically into trouble. If he knew Remus was going down the tunnel he knew Poppy Pomfrey was as well, so he knew that whatever was happening, was happening with the approval of the staff.
Thirdly, he had the right to find out whether he *or Lily* was in danger from a werewolf. The fact that the staff were involved didn’t mean that what was going on was safe, any more than it would be in Harry’s day. Nor is curiosity a capital offence. How would those who think Snape deserved to be killed feel if Hagrid had been executed for his interest in giant spiders?
Fourthly, the idea that Snape necessarily broke curfew is a fanon myth. If this happened in winter, full moonrise could have been as early as 4:30pm.
Fifthly, there is no reason to think that he knowingly walked into danger. He would presumably think that the tunnel led to Hogsmeade (which in a sense it did, since the Shack is on the edge of the village), not to a dead end, and that Remus was being taken *out* at the other end and then to a safe place.
Sixthly, there is no doubt that he was in extreme danger, because Remus says James put himself in extreme danger to save Snape.
Now, this is complicated. There is no indication that Remus’s howls are ever heard from under the ground or under the tree, and it would be very risky to have him loose in the tunnel, where he might barge out before the Willow could hit him, so we can I think assume he is normally confined to the Shack.
The tunnel is about half a mile long and very low and narrow, and a significant period before reaching the Shack it turns upwards and ascends a long flight of stairs which ends either in the floor of the Shack or very low down in the wall. This combined with the low ceiling means that it would be impossible for a person who was in the tunnel itself to see the top of the stairs: they would have to be actually on the stair. Nor would it be possible for a person who was on the stair to see Remus in the Shack unless they were right at the top of the stair looking in, or Remus was right at the entrance looking out - and then only if they were close to the top.
Neither scenario sounds much like Remus’s claim that Severus glimpsed him at the end of the tunnel, and in neither case would Snape have been in much danger. We know he didn’t open the door (or ward or trapdoor or whatever) and go into the Shack, because aside from being stupid that wouldn’t remotely resemble Remus’s description.
The implication, therefore, is that Sirius loosed Remus into the tunnel, meaning Sev to be killed or infected, and showing a startling lack of consideration for Remus, as well as for Sev. The fact that he is still bragging about it 19 years later, at the mere mention of Snape’s name, shows just how malign and murderous Sirius was. How would you feel about a real bully at a real school who tried to trick one of their classmates into going into a cave where they knew there was a grizzly? Would you say it was their victim’s fault?
[But allowances should be made for the fact that it happened round about the time of Sirius’s break from his family, so he may have been having a mental breakdown, and later on after 12 years with the Dementors he was *definitely* having a mental breakdown.]”
-Claire Jordan, Quora, Is Snape to blame for the Whomping Willow incident? (Warning, lots of victim-blaming bs in the answers)