We already have it in the Netherlands and I think it is a good thing. I know several people who chose for assisted dying when they were terminal and I think it protected them from a lot of unnecessary suffering.

There are some laws in place to prevent abuse. For example, there is a second, independent doctor assessing the situation to make sure conditions are really met and that someone is really terminal and deciding this from their own free will. The patient should be able to reconfirm that they really want to get euthanised before it happens. I think this is a good thing, but sometimes it is difficult when people with dementia clearly have stated and written down officially that they want assisted dying in certain circumstances, but they are not able to reconfirm because they lost their ability to understand.

In some cases you can have assisted dying when you suffer psychologically without any outlook of improvement (i.e. you have tried all treatments etc). However, there are waiting lists for those, which are quite long. My sister was on such a waiting list because she had anorexia. However, she died from starvation before she could be assessed. I am still a bit in doubt whether it would have been a good idea for her to get assisted dying. I still was hoping and thinking that there could be ways for her to get better.

Maybe the doctor assessing whether she would be approved for this would have thought the same, maybe not. She died anyway, so maybe I was wrong. In any case, I am not completely against euthanasia in case of psychological illness, as people can suffer from that equally as from physical ailments. However, you should be extremely careful and it should be extremely clear that there is no other solution at all anymore.