Opiates and opioids blunt emotions. This is demonstrable fact and is the case for everybody who uses them regularly. They block feelings of all kinds. Actually not quite block but blunt - you feel but not really feel the way you would otherwise. It's one of the real problems with opies. Aside from all the addiction and stuff which is also a bit of a shitter.
I wouldn't agree that alcohol allows you to feel true emotion, I'd say alcohol makes emotion self-indulgent. Whilst the emotion may well be completely accurate it's exaggerated and made to feel all-encompassing. Speaking for myself I know that if I'm feeling a bit down then drink I'll end up feeling horribly down. In the past this would often end up in resorting to extensive self-harm. I almost never self-harmed when sober or on other drugs. When I feel happy and drink I tend to become hyperhappy and end up acting like a complete moron. Perhaps not as bad as slashing fuck out yourself with broken glass and razor blades but still a bit awkward when having to face people I was acting an utter bellend with the night before. Not saying I never do anything like that on other drugs but don't think I get quite as nauseating as I do when drunk. This is but me but I do believe that can be generalised to a certain extent. Not real emotions, exaggerated emotions. They are equally as unreal as blunted opiated emotions. Just more flamboyant.