Will it? Says who? We will lose come coastline for sure. But on the other hand, we'll presumably have areas which are currently too dry to be arable, which then become arable. And we'll have arctic tudra where nothing grows currently, which in a century may well be fertile and highly productive. I think it is far from obvious that we will be able to grow less and will have less food to live on. And who knows what technology we will have to produce synthetic meat etc.
Overplayed as an argument IMO. The whole thing smacks to me of "We need to do something about climate change, so how are we going to justify it". Scholars looking for reasons to justify their beliefs. I dunno - maybe you have a point on this one, I really don't know. But climate change is gradual and we'll have decades - tens of decades - to adjust.
People are far too quick to point at a forest fire and say "look, climate change". If politicians and scientists were honest about the whole thing, I wouldn't have a problem with it: i.e. Climate change is happening and we must take steps to try to moderate the effects. But far too many of them are not honest. Either that or they are idiots. They try to pretend the world is coming to an end, in order to try to shock the gullible into action. Or they genuinely believe the world would come to an end, in which case they are simply idiots. When did the BBC ever put up a chart like this: