You realise pro-euthanasia is a left-wing position?

I’m centre-left, so in this circumstance you’re the raving left-winger (along with everyone else here).

Let me distill your argument

Premises

1. Ducks can suffer
2. We can alleviate duck-suffering by killing said duck
3. It is permissible to kill ducks to alleviate their duck-suffering

Then you construct an analogous argument

4. Humans can suffer
5. We can alleviate human-suffering by killing said human

Conclusion Because it is permissible to kill ducks to alleviate their suffering it is therefore permissible to kill humans to alleviate their suffering.

Now the error is actually on premise 3. You make a deductive claim that it is permissible to kill ducks because they are suffering. But this is faulty, it is permissible to kill ducks regardless of whether they are suffering, because as cited before they are ducks. Therefore your claim that it is permissible to kill ducks who are suffering is at best indeterminate, we would need to show that it is uniquely permissible to kill ducks only if they are suffering because the corresponding circumstance in humans is creating a unique exception to prohibition against active killing.

TLDR: Pretty sure either I know your argument better than you do OR you are awful at communication.