I strongly feel that legalising euthanasia is not a good idea. I think that we only need to look at the countries that have gone before us to see the potential dangers of legalising it. There have been cases in recent years of people who have mental health issues, non-terminal illness and children all undergoing euthanasia in European countries. While these things tend to start being strictly enforced as only adults with full capacity and significant life limiting conditions precedent in many European countries suggests that it doesn't stay that way. I think to protect the vulnerable (the elderly, those with mental health issues etc) I could not support a change in the law.
This is an issue which is very close to my heart. I am in no way insensitive to the suffering that people are going through. My mother passed away six and a half years ago having had an aggressive form of multiple sclerosis (some of the legal test cases have involved the exact condition that she had). In the end she was unable to move her arms or her legs and if she had survived her final hospital admission she would have required feeding with a tube. I know that some of the things that people are facing are horrendous and I know that there were many times where my Mother would say to me that she wished she was dead. I also have to face that in the future I have a higher risk than the general population of developing this condition (though it is still a reasonably low risk). Through my work I have spent time with many people who are in the last weeks, days, hours and minutes of their lives and I have tried my best to support them and their families. So I realised that people are suffering and by no means am I trying to minimise that in any way.
However much of the suffering that they experience can be minimised with good palliative care and good social support (with regards to appropriate care packages as well as emotional support for the patient and their families) and in extreme cases there is always the option of terminal sedation. There are also issues which it would be hard to legally protect against like elderly or vulnerable people being pushed into making this decision (either intentionally or unintentionally) by family members and feeling like they are a burden (to give just one example). Things may start of rigourously with two long appointments with two doctors however one only has to look at the way that abortion is done now to see that things are shortened and corners are cut (many women don't even see two doctors any more the first doctors report is just approved by a second who doesn't meet the lady), this wouldn't have been the case initially but over the course of time things become more lax.
I think there are very few good secular arguments against a hypothetical system where an adult with a terminal condition with a short prognosis, who has full capacity and has been fully counselled chooses euthanasia. However in my mind it is a big step to go from that to actually legalising it. As from looking at the precedent set by other countries who have started down this path a lot of them have now gone further than I would personally feel comfortable with and I see no reason why we wouldn't also end up with the same situation a few years into the future.