1. Pre- extended cut Shepard being dead is no an opinion. He has no way to being able to servive in the long run. His dead, fact. If it's post- extended cut then you can say he's alive.
2. But it being locked did not make the ending worse. Blaming the mp for the issue of the sp is pointless.
And there is no need for convicing. ME3 mp effect the sp with it's exports. DAMP has no exports what so ever in the sp. So until it does you have nothing to worry about.
1. Its the same game, he's either dead in both or neither. I saw the ending pre EC, he was alive in my opinion. It certainly isn't a fact that he's dead.
2. I think you are being deliberately obtuse. Being locked didn't make the ending worse, it made SP in general worse, because the best ending was locked. This isn't about the endings, it is about the campaign. The ending to a campaign is one of the most important parts, it is what people remember the longest. For ME3 the 'best' ending, and the only one where Shepard might have lived (again this is an opinion, there are no facts about this, despite you thinking you know best) is locked behind MP. This makes the campaign, as a whole, notably worse, because it ends on a different note than it could have had MP not effected the SP campaign.
But anyway I doubt the argument about MP killing SP will go away until people have a few days to calm down and recompose themselves. Then maybe we can have some actual conversations with them about why MP isn't going to kill SP.