The numbers of Protestants in the country declined sharply in the decades after Independence. Do you think that they just chose to leave their own country? What do you think happened?
In the 4 years after Independence 40,000 Protestants fled the country in fear as a new State was constructed which excluded them. Around 150-200 Protestants were murdered and there were mini pogroms around the country, particularly in West Cork. In Bandon and Dunmanway there were 13 murdered in one night in April 1922. The youngest was a teenaged boy.
I have no doubt that the sectarian killings of Protestants drove many to leave the areas but when you talk about ethnic cleansing, and associate it to the new Free State, it is simply not true. Neither the Stormont or Dublin administrations implemented policies, covertly or otherwise, to ethnically cleanse Protestants or Catholics. You have inferred that Protestants fled the country in fear as the new State was constructed to exclude them, that this equates to 'ethnic cleansing' - this is a falsehood.
Fleeing a State in fear of persecution or discrimination is not ethnic cleansing - it is fear generated on perception, whether real or imagined, or exaggerated.
What was happening in Northern Ireland was worse but that in no way excuses what happened in this country. But the actions of both States in the years after partition look like
ethnic cleansing to me. The net result here was a reduction
On the second paragraph of that link "
Although scholars do not agree on which events constitute ethnic cleansing"...so perhaps advisable we try not to define it? You have given your example, you might equate it to this population decline of Irish people that includes Protestant and Catholics?

We'd probably still be British so I'm glad they did since I'm a Republican though not a Nationalist.
Ireland was never British. Under British rule, yes, but as part of the UK of GB
and Ireland, Ireland was never British save a minority that identify as such.
There's a very strong case to be made that we would have achieved independence if the Rising never happened.
True, but it is all speculative. However, I would have rather the British stood firm against the Unionists and upheld their own laws when it came to the rights obtained by Ireland through democratic and constitutional means.
A poll in 2015 asked people in the Republic if they were in favour of a United Ireland if it meant they would pay more taxes, 31% said they were, 44% said they would vote against it.
31% in favour and 44% against. 25% undecided?
I would say that is very positive figure for a UI. Think about it, the question was "
if it meant paying more taxes"? 33% said 'Yes', with 25% undecided!!
I can only imagine that if the poll were tomorrow, sentiment and identity would surge and the tax question would be obliterated.
That's not a decline, it's a proportionate increase in the Catholic population
Versus a stagnation of the Protestant population, what happened?
The point being, that there are many, many factors that may be attributable to a population decline. If the Protestant population couldnt grow in a Protestant State for a Protestant people, what hope in a Catholic State?
It takes time to unwind such structures
"such structures", such as internment without trial only takes a Ministerial order to release all those in custody that have no charges pending. It could have been done in the dead of night, similar to how it was introduced.