I have a feeling we're not going to agree, but I still have some objections to the methods it sounds like you're using.
"But you can provide a link to your [Stackoverflow] profile when you apply for a job so others can see what comments you've made. This gives potential employers an insight into not only whether you're knowledgeable, but also whether are you able to help others in a meaningful manner."
I don't think that's a useful yardstick. In order to earn a job at your place, I not only have to be good at writing code in the systems you are using and solving the problems you have, but I also need to have volunteered a lot of time answering others' questions and proving myself to be a good teacher. Are you trying to hire a teacher? Because that's the skill you're measuring with this. If you want to see that the candidate can explain a technical thing, ask them to explain a technical thing of your choice during the interview. This demonstrates that A) they can explain technical things, B) they know about the thing you chose, so you can tailor it to something you want them to know about, C) their skill can work with people of the knowledge level you have, rather than someone who may not have a clue, and D) if you aren't sure yet, you can ask them about something else.
"Regardless of whether they're directly relevant to the job you're applying for, [GitHub repos] will give an insight into your abilities to structure and design code."
In my original example, I pointed out why that could easily be misread. I gave an example where the code you would see is the stuff where code is likely to look of poorer quality and where the person has little experience, thus giving an unrealistic idea of their quality.
"If they're personal projects, they will show you have a genuine interest and passion for software development outside of it merely being a way to pay the bills."
This is a problem I didn't deal with last time, but let's do it now. Why does someone need to spend a lot of time on writing code outside their job in order to qualify in your mind? If you're hiring an architect, you generally don't require them to show you the several hobby building designs they have. There are several reasons a candidate might not have a lot of contributions for you to comb through. They could be limited by a legal contract that prevents them from developing or releasing things outside work. They could have a job with long hours and obligations outside it such that they don't have the time to maintain a complex project outside work. Or they could have interests other than computers and still be entirely capable of doing the job you want.
"Whether you agree with them or not, a potential employer should use all tools available to evaluate a potential candidate,"
I disagree. A potential employer should endeavor to establish whether the candidate has the needed skills without being creepy and without requiring unreasonable steps on the candidate's part. The definitions of creepy and unreasonable are subjective, but it's easy for "all available" to start spilling over into them. I've seen employers who do the creepy investigation into anything they can find with the employee's name on it, which has caused problems for people who share names with other people. I've also been asked for everything under the sun by companies because they couldn't possibly know whether I can develop a system unless they can talk to everyone I've ever worked with back to jobs as a student. In each case, they had the ability to ask me to prove something but chose an unreasonable method instead. I don't work there.