Landsea's point is that the IPCC was making alarmist official statements that had no basis in fact and ran counter to the underlying scientific literature. Landsea was the relevant expert on the subject and even he couldn't stop the fear-mongering; he quit because he didn't want to be associated with it. The issue he quit over was that there really wasn't an "accelerating rate of catastrophic weather incidents" to the degree the IPCC was trying to claim at the time.

On good things we can expect: The main measurable good thing we can expect from the next 1-3 degrees of warming is increased agricultural productivity. In the northern areas where most of the world's food is grown, warmer average temperatures means a longer growing season which makes it easier to feed the world. (It also increases the range where we can grow crops and makes winters less bitterly cold in places like Canada.) Closer to the equator the warming part doesn't help so much but the extra CO2 makes forestry more productive - it helps trees grow better due to CO2 fertilization.
(My main source on this is the AR4 IPCC report - I haven't read AR5 yet.)

Also: many more humans die each year from excessive cold than from excessive heat; a planet with less bitterly cold winters is a more habitable one.

Also: being warmer puts us a little further away from the next ice age. Climate always changes; given the choice, I'd rather it get a little warmer than a little colder. (There is no reason to think the temperature in, say, 1990 was optimum for human life worldwide. We don't need to return to that, nor do we need to keep it where it is now.)

With regard just to sea ice it's not "oscillating between extremes" so much as there's been a shift over time as to where more sea ice collects on the planet - more in the south, less in the north. Changing sea currents and weather patterns can do that over long cycles. When alarmists look at growing sea ice in the south they dismiss it with "oh, the currents have changed" or "oh, the weather patterns have changed" or "yeah, but ignore that and look at the LAND instead!" but when they look at shrinking sea ice in the north they tend to insist it's due to warming and only that; I'd like to see a little more consistency.

SkepticalScience is not a reliable source - it's a propagandistic site run by a cartoonist, not a scientist - but in this case that's not a factor: argument 25 at that link is about sea level rise. Since I agree that sea levels have (very slowly) been rising over time, I'm not sure how that's relevant. (FWIW, I also agree that measured temperatures increased in the last half of the last century and that CO2 is a greenhouse gas and that some recent warming has been the result of human activity.)

> HN is the last place I would expect to find myself fighting against climate change skeptics

The article you wrote suggested in passing that the planet could become uninhabitable in mere decades because we've passed a bunch of "tipping points" - you're bound to get some pushback if you try to make wild-eyed claims of that sort. If you want to say stuff like that you should try to figure out where the claims are coming from, whether there's any science behind them, and whether the science is any good.