Think about it this way. Say you are volunteering for a non-profit. You obviously don't have to do it and could just chill at home instead. But once you have agreed to say take a volunteer shift on Saturday, you are obligated to show up. Obviously no one can really stop you from skipping, but it would look bad on you and may get you banned from the non-profit. Along the same token, you obviously shouldn't steal from the non-profit, or say randomly beat up the customers/clients. If you accidentally set the building on fire which ends up killing 5 people, I would also assume you would help in some fashion to clean up.
Just because you are doing things for free does not mean you don't have social responsibility for your actions. You don't have to work, but just saying "oh my software ends up compromising everyone's computer? sorry not my problem" is seriously misunderstanding your role (I'm not saying that Collin is doing that). Similarly, if I just randomly slapped you in the face, I might have done it for free, but you would also probably be pretty pissed at me and expect an apology.
Just want to point out that this isn't a typical "demand underpaid open source developers to work 24/7" issue here. This is a unique circumstance where his action has directly resulted in this happening. I feel bad for him being guilt-tripped to add a maintainer after reading through the old threads two years ago, and as I said I don't want to burn him at the stake, just saying that saying he has no responsibility to help at all is really a bad take.