I don't think very many users want Fentanyl at all; short high, little to no euphoria. What users really want is diamorphine or similar, which is way less dangerous, but fentanyl is commonly used because it's cheaper to produce. Pure, consistent drugs would allow users to dose correctly and avoid overdoses.
If you think alcohol should be legal then why not opioids? I just don't see how people can square these view points. We admit that alcohol can cause all sorts of health issues, including addiction and abuse, but it is legal anyway. And as a result it is well regulated (we know what we're getting) and it is easy to obtain (we don't have to deal with shady people in potentially dangerous situations). If someone is an alcoholic, then their family may ask them to seek help, but most of us will just ignore it because it is that person's problem and is not affecting us. There isn't any restrictions on alcohol content in most places - you can buy 180 proof grain alcohol just as easily as weak beer.
So why not treat other drugs the exact same way? There is no way to be logically consistent about this UNLESS you think that alcohol should also be illegal.