Hmmm... I know myself to be rather critical when it comes to things like that, so you'll probably have filter my personal opinion appropriately, but the problem I see in relation to that "by-line/side-note" is that it might serve as a base for "worse things to come".
What I mean is: today, it's "I recommend a donation to the OpenBSD foundation.", but tomorrow others might transform that option into a "please sponsor my project by visiting this paypal url". Yes, I know that's a bit of an extreme assumption. On the other hand: this is the internet and it is likely that sooner or later, someone will post something alike.
When that happens, we indeed will have to know if we want to try drawing a line somewhere and constantly defend that line, or - what I personally think is best - simply remove such non-related things as it's nothing else but (what I would call) "noise".
In the end, removing such a by-line/side-note (or whatever you want to call it) would not be much different from how we handle "thank-you" messages, "signatures" and "footers": we remove such things to keep the focus on the content, thereby safeguarding the overall quality of the Q&As at Crypto.SE.