1.The words "didn't bother" have relatively little relevance here. With the amount of emigration foisted on this country many many people were unable to vote. Do you think they should book flights back to Ireland just to vote?
I for one have certainly done so if I was abroad, not that I necessarily advocate that approach. I sincerely doubt though, that 50% of the electoral register has emigrated. That would amount to more than 1.5m people (excluding minors). Even if a third of that number have emigrated it still doesn't account for the majority of the non-voters -which would be on the high side frankly since net migration in this country has been in the region of 30k-40k pa and only in the last few years.
2. There would be a fair amount of people whom for some reason or other could not vote either i.e. sick people, hospitalized, holidaymakers abroad, and the disgruntled.
Disgruntled is not a reason you can't vote. Disgruntled is a reason you decide to stay at home and sit on your hands.
Holidaymakers equally make a conscious choice to disengage and prioritise their holidays over their civic duty. Again this is unlikely to consist of 1.5m voters and their children on any one day, it might be 10,000-30,000 so I would argue that the number of voters choosing holidays over voting is vanishingly small in the scheme of things.
That leaves sick and hospitalized. That would consist of people who have chronic conditions and those who have acute conditions. Of the two, logically only those with acute conditions are likely to be unable to vote due to illness or injury. Again it is unlikely this constitutes a significant number of people on any one day. I doubt that 1.5m people are in hospital at any one point. I doubt that 10,000 are in hospital with acute conditions at any one point. Those with chronic conditions generally can avail of the postal vote - so if they chose not to vote, they are also failing in their civic duty. There would be a cohort in here who no longer have the capacity to vote due to mental decline but again we are not looking at a significant amount of people to make a good dint in that 1.5m you need to make up to validate your argument.
3. I look on those who did not vote as people who were genuinely protesting against a choice of politicians who would scam them as against those who would rip them off. I fully understand why people would not vote and empathise with them.
I look on them as an undistinguishable and unknowable morass of different reasons - they have no voice because they choose not to speak. Unlike you I don't think most of them have left the country, are sick or are "protesting". I think if you want to protest you get out there and vote. I think the vast majority of them are indifferent and frankly lazy.
4. Those who spoilt their votes are included in my 3rd point above. In the light of our "stroke" politicians it is obvious that the voters were ensuring that their votes would not be used. We've seen what politicians do with their travel claims etc, God only knows what they would do with "available" votes.
Those who spoil their vote are genuinely and consciously protesting. Whether I agree or disagree with their protest is not an issue, I respect them and their choice. They have voted. (Even if they deface their vote in [broken link removed]

)
Then we have the unopinionated braindead; those who will vote down party lines no matter whom or what is put up for election. Do you think these deserve more respect than those who for one reason or another did not vote?
Actually yes I do. Chances are they are opinionated and thankfully they are not "braindead". One may not agree with their choice but they believe in their party - if they choose to vote along party lines then they are as entitled to do that as the person who chooses to spoil their vote. What you are missing is that
they agree with their party. That is a choice. That is an opinion. That is a valid reason to vote for the candidates they choose to vote for.
It is very easy to judge people while looking outward, but when one looks inward the playing field looks completely different.
No point in looking inward. We are not all wired up to some brain reading machine which decides the outcome of the election based on our collective inner meanderings - and for the life of me I cannot think why anyone would want such a nightmarish dystopia. We either get out there and engage or we don't.