Your argument collapses two separate questions: “Is someone consenting?” and “Is something morally permissible?”
Free consent matters, but consent alone cannot make an act morally acceptable. We don't normally argue that something becomes ethical simply because everyone involved agrees to it. The relevant question is whether there are independent reasons why the act should be permitted, especially when the act involves intentionally causing someone's death.
And “doctors are willing to participate” doesn't solve that problem either. Doctors can sincerely disagree about whether euthanasia is ethically justified. Their willingness to participate is evidence that they accept the practice, not proof that the practice is morally right.
The second claim is even more self-defeating: “No one decides what is moral. It is a personal opinion.” If morality is only personal opinion, then you have no basis for saying assisted dying is morally acceptable either. At most, you can say “I personally approve of it.” You can't move from personal preference to the conclusion that there is no moral problem with it.
In fact, saying “there is no problem” implicitly makes a moral judgment. You're not merely stating a preference; you're claiming that other people ought to regard the practice as permissible.
So the argument needs to do more than appeal to consent and personal opinion. It has to address the actual ethical questions: whether consent is genuinely voluntary in every case, whether vulnerable people can be pressured, whether intentionally causing death is morally different from allowing someone to die, what safeguards are necessary, and whether there are circumstances in which consent should not be sufficient.
You can absolutely argue for assisted dying. But “they consented, doctors agreed, and morality is subjective” doesn't establish the conclusion. It mostly avoids the difficult ethical questions that actually need answering.