On the other hand, this one is incorrect, so it's a bad trade-off no matter how you put it. Besides, the meaning of "stellar mass density" ought to be obvious

On the other hand, this one is incorrect, so it's a bad trade-off no matter how you put it. Besides, the meaning of "stellar mass density" ought to be obvious to anyone who's gone through high-school level science classes, even if they're not "into" astronomy. Even if that weren't the case, it's pretty easy to look up a simple explanation of the term. I doubt someone who isn't willing to put even that tiny amount of effort into it would even bother reading popular science articles in the first place. To put it another way: it takes less time and effort to figure it out if you don't know what it means that it takes to even read the article. The overlap between "people reading the article" and "people who don't know what SMD is, can't figure it out from the name, and aren't willing to look it up" is unlikely to be too high. Optimizing for lazy readers isn't good scientific journalism, it just makes the experience worse for interested readers -- the ones who are willing to do things like pay for a subscription, for example. It's a bad trade-off to make.