"Has been abolished in 1966" says that it was abolished in 1966 and it remains abolished today.
"Was abolished in 1966" says that it was abolished in 1966, but it provides no information about whether it might have been reinstated later and it might continue to be enforced today.
So in this case I believe that the other poster was correct in using "has been abolished in 1966".
That meaning would be expressed as "has been abolished since 1966", unless it is still 1966 when the idea is being expressed, in which case "has been abolished in 1966" works instead; "has been abolished" is a present perfect (passive voice) construction so "in <past time period>" doesn't make sense with it, while "since <past time period>" or "in <current time period>" does.
Specifically, using the combination "has been ... in". Either "was abolished in" (simple past in the passive voice) or "has been abolished since" (present perfect in the passive voice) would work (simple past describing the event of abolition, past perfect describing the continuous state of having been abolished from the point of that event up until and continuing through the present moment) would work.
Using “has been” here makes it immediately clear that you’re a non-native English speaker, unless you’re speaking some dialect I’m not familiar with.
Usually, we use the perfect (“has been”) with time intervals that include (or asymptotically approach) the present. We use the simple past (“was”) with time intervals or points that are closed and are clearly sepatated from the present.
For example: “I went to Lebanon in 2015”. 2015 is a specific point in time. But if I don’t include a time, I’d say “I’ve been to Lebanon”. Even though this was in the past, the fact that I don’t mention a specific time in the past means it implicitly includes the present, because I’m describing my current state: I’m someone who has been to Lebanon.
And, if I were in Lebanon now, for the first time, I could say “I’ve been to Lebanon”, and then it really does concretely include the present!
To illustrate another edge case: I’d say “my father has never been to Lebanon” but “my grandfather never went to Lebanon”. Because my father is still alive, but my grandfather is dead. So any statements about his life are automatically about a closed interval lying entirely in the past.