It's not murder. Murder is the state's language to describe killing that breaks their monopoly on violence.

unless the rapist is committed to and able to participate in accountability, consequences, and reparative work, it is statistically unlikely that even a rapist who feels remorse, guilt, and/or a desire to change their behavior will not commit intimate violence again.

Many rapists in fact do not have these opportunities, either due to a lack of social supports for victims to have their perpatrators held accountable, lack of desire by the victim(s) to facilitate or participate in those kind of processes (which is totally valid of course), or even in some cases being enmeshed in a cultural context where they cannot disclose their past without being subject to immediate and far-reaching ostracization. Thus, for any number of reasons even a rapist who wants to change their ways is going to remain a huge fucking liability to any organizing effort, due to the lack of conversation or community projects that are designed to deal with their toxicity.

In fact, to the contrary most rapists are enmeshed in a society which not only excuses, but even valorizes their behavior. This happens not only in dominant society, but also in radical subcultures. So the rape becomes a positive thing, or one that can be invisibilized if inconvenient. In that social context, it is very rare for the rapist to even acknowledge their behavior as negative, or as what it is, let alone have a desire to change themselves and their relationships with others.

Thus, any rapist who has not gone through some kind of effective, victim-centered community process (which is basically all rapists, statistically) has a very good chance of hurting someone again, particularly people they are intimate with. Even people who do go through this process frequently commit violence again. Rapists are a clear and present danger, which necessitates cutting rapists out, which in turn fuels their dangerous toxicity, and in some cases even their desire to commit further violence on populations who they feel "wronged them" by exiling them. And so the cycle of violence continues.

Nonetheless, this is also why it is justifiable to kill rapists. If there is a broad social context that prohibits serious restorative justice work (generally true across the globe, and from what I hear about South Asia it sounds pretty true there too), the rapists are in power. Non violent methods have failed dramatically. If people are going to start striking back, it's assymetrical warfare against a much more powerful target, and deserves the support and solidarity of those who oppose rape culture.