Is it wrong to murder a loner with no family if you don't make them suffer?

Most people don't actually believe the boo-hurrah theory of ethics (as it's called by its detractors).

Many would.

Kangaroos will overpopulate and destroy habitats of other animals through overgrazing if they aren't hunted. The government sets a hunting quota, and if it isn't reached, they organise cullings. Culled kangaroos are dumped in ditches or mass graves to rot. It's better for them to be hunted so someone benefits from all that death.

Bees can fly and make intelligent decisions about where to put their hive, so beekeeping is kinda consensual. As much as a bee can consent, anyway. If a nest location is unsuitable, bees will swarm and find a new nest. They're used to planning ahead by months and judging local resource conditions. However, some beekeepers clip the queen's wings to prevent swarming, and I think this is completely unethical and inexcusable. But outside of that, the way beekeepers prevent swarming is by helping their bees and giving them a good life. In fact, taking honey can even be good for the bees! Sometimes bees will fill all of their comb with honey and won't have enough space to raise eggs. It's called being honeylogged. Honeylogged hives will swarm to go find a new nest, just cause they had too much honey!

Further reading:

https://en.wikipedia.org/wiki/Kangaroo_meat#Kangatarianism

https://www.reddit.com/r/DebateAVegan/comments/108w7tt/the_great_honey_debate_is_honey_vegan/

It seems to say you would be unclean to touch a dead animal. That means you need to take a bath and wait until evening to be clean again.

I think this is before the invention of soap, so being ritually unclean meant that other people aren't allowed to touch you for a certain number of days (and then you need to offer a sacrifice in the temple or something), or in some cases like touching a leper, the priest has to examine you at the end of the unclean period to declare you clean.

It's heavily disputed whether those translations are more accurate rather than just reading nuance where none exists. Some translations also interpret it as specifically about pedophilia, but again, they may or may not be more accurate than simply translating it as all M/M sex.

The very fact of the whole text being:

1. In my skeptical opinion, likely invented by ramblings of a nutter, and the book was written as an attempt to write history by those who listened to the town crazy;
2. (Western editions) Translated multiple times - (roughly) Hebrew 'Torah' (the 'Nevi'im' and 'Ketuvim' came later) to Greek 'Septuagint' then to Old Latin 'Vetus Latina', then revised using the 'Septuagint' and translated directly from the 'Hebraica Veritas' to make the 'Vulgate', and into modern languages (true English, French, and German originally) 'Bible' by multiple groups;
3. As well as many translators there are countless individuals who either evangelise or simply read for themselves, each with their own unique interpretation of every verse;

makes me suspect that every single translation has some error, and because I cannot read Hebrew I'll never truly know. Even what used to be the most trusted digital translator, Google Translate, now uses AI to interpret and adjust the wording, making the translate service more useless than it already was. FWIW, whenever I need to consult the English Bible I prefer the King James Version (1769 revision, not the NKJV), not only because I love the language style, and that it is in a language I can read, but it is translated into English from Hebrew (Old Testament), Latin (Apocrypha) and Greek (New Testament), and in my opinion if there are deviations from the Hebrew 'Masoretic Text', the KJV will have less errors than others.

A good read of the women involved in one translation: Paula and the Latin Vulgate

So then if I consent to someone fucking my corpse after I'm gone, it becomes morally OK for them to do it.

A corpse is not a sentient creature. Former sentience is not the same as sentience.

A corpse should be treated like the person it was, so it still needs consent otherwise you're still raping it.

That's your opinion, and it's completely valid, but what's your justification for why someone else should agree?

Extending your logic to make my point, if a corpse is blurring the line, what about brain dead coma patients, especially ones that are infertile? Are they ok to rape? They're alive and can't reproduce, so what's the difference, right?

Well, they're alive, for one. Corpses by definition are not. And what we think of as "brain-dead" is the long-term and potentially permanent loss of consciousness and therefore sapience, but sentience is a bit harder to disprove.

Your standard seems to be "current or former sentient beings," which is consistent, but you haven't given a justification for the "or former" part. Current sentient beings experience suffering, so that's a pretty good reason, but corpses don't.

Exactly, you can construct what ever moral framework you want to, sky daddy or not.

I have the great privilege of living in a society with socialized Healthcare, so these questions do come up from time to time.

The lifetime Healthcare costs for people who have conditions which can be mitigated by lifestyle choices is a real thing. Smoking, being an obvious example much less touchy than obesity. Even if I'm extremely comfortable with the slice of my taxes that go to Healthcare... wouldn't it be great if we got to spend less on smoking-related issues, and could instead buy more MRI machines. Merely pay for more doctors? Nurses? Expand the treatments we can even offer?

Just because they're abstract, doesn't make it any less of a question of morality. I don't see any moral difference between the contaigen and smoking from the perspective of the personal responsibility of maintaining the overall health of your society. One is just accepted by society.