If it was layoffs, you just do them. You don't explain and you don't create a large number of now-ex employees going to Twitter to say why you suck.
If it was downsizing to something more comfortable for the founders, again, more easily done with the same buyout package, and much less of a black eye by just saying "we want a smaller company, so we're putting our money behind doing right by everyone as we get what we want."
If it was getting rid of agitators, it's actually easier to fire them and deal with the lawsuits. Most companies have some amount of ongoing legal expense, and getting sued isn't that bad if you're not smoking-gun discriminatory. You can always file a lawsuit, but it's much harder to get somewhere with a lawsuit, and there's a reason corporate attorneys get big bucks--that Basecamp has to pay.
The best explanation is the most obvious one: they made a colossal blunder in handling this and have footgunned their company badly enough that there will now likely be a second wave of buyout accepters who are people who don't want to stick around to clean up the mess.
>This term has historically been used in America to describe black people who were considered to be acting above "their place", and is considered by some to have racist connotations when applied to black people and other people of color; sometimes, arrogant or presumptuous, invoking the same idea, are used as codewords for it.[3][4][5]