As always the devil is in the details, or in the interpretation if you like.
First, it is not entirely clear what blameless (anupavajjā) means in this context. Upavajjā normally has the very broad meaning of “criticism”. It does not necessarily imply bad kamma or immoral behaviour. In the present context, the criticism is against “taking up another body”, i.e. getting reborn. This doesn’t really say anything about the act itself, whether its bad or good kamma. If we take the sutta at face value, it is rebirth itself that is criticised. In other words, if you still have an opportunity to practice, you should take it.
In many cases where people are suffering tremendously and are close to death, however, I think there is often very little or no scope for practice. At a certain point the pains and problems - especially for ordinary people - may even be detrimental to practice. You might get angry that the doctor or your family is keeping you alive when you have no quality of life and there is no prospect of recovery. Making bad kamma towards the very end of your life is certainly not going to be helpful. Staying alive only has value to the extent that we can use our life for a purpose.
I can only agree with you, however, when you say that we should not glorify suicide. It is an imperfect option to be used only in difficult circumstances, and only after careful consideration. The problem is that sometimes there are no good options. We are then left with choosing the least bad one.