The issue of liability can be solved with consent, just as it is in the randomized trial. The number of patients to receive the treatment doesn't seem to affect liability, nor does the cost of the treatment.
Also showing product safety is generally much easier than showing effectiveness, and different people (especially those with a terminal condition) have different tolerances for risk.
The question your raise is whether you learn something from non-randomized trials (which I agree are the gold standard procedure). If there is a very lethal disease (that we're able to test for but not treat), and the people taking the treatment (in various locations, conditions, etc) fare significantly better, while the people who don't continue to die, can you draw any conclusions as to the effectiveness of the treatment? I think you can make inferences, although with lesser confidence.
The question that follows from that is, if you are a doctor or producer and have such a treatment, is it ethical or desirable for you to withhold it? That seems selfish to me (putting your preference for experiments over my preferences as a patient).
Is it ethical for prohibit the doctor or producer from delivering to consenting patients? To me, that seems paternalistic and unhelpful (not to mention of questionable political authority). It would seem much better to help inform the patients and give them support for their own choices.
As I suggested in another comment you could imagine a two prong approach: customers are allowed to get a safe but unproven product, or participate in experiments with some compensation/incentives. So you could still conduct experiments on people who accept that bundle (risk and compensation including the satisfaction of knowing they are helping science).
Whether people SHOULD participate in those experiments and therefore those experiments SHOULD continue to exist doesn't seem a categorical/universal question to me. It seems a question of preferences (demand). Assuming enough people demand the extra confidence and rigorousness, and enough people are willing to take the risk of receiving a placebo, then they will exist. Otherwise you are imposing your own will and preferences on people, which hardly seems civilized or peaceful.