I'll sure try! Here's a picture of what I was visualizing, but explaining why it matters will take some words: https://imgur.com/a/MggDJ I chose weird colors deliberately.

The diagonal line represents policy, or the wedge. In reality it's not always a straight line.

Stymieing bad people is what happens in the left square, empowering good people in the right square. (This left / right correlation with real world political parties is a coincidence. Liberals are often arguing positions to empower good people when conservatives opposition hinges on a claim that they're stymieing bad people, just for different policies (gay rights, abortion and marijuana come to mind).

But for a real world example,
The Stoneman Douglas school shooting occurs:

Side1: Restrict gun purchases.

Side2: Give teachers guns.

Here's how I look at this in the context of the portrait. Pink represents keeping guns from bad people, the orange side represents good people having access to have guns. Right down the middle is an aspirational fantasy world where bad people have zero guns and all good people can have all the guns they want. A vertical line on the far right side represents everyone having unrestricted access to every kind of weapon, a vertical line on the far left side represents no one having any weapons at all.

Both sides of the wedge, as it is today, prevents some good people from having access to some weapons and allow a some bad people to have access to some weapons. Flatly restricting guns marginally will marginally reduce the access to guns for both good and bad people. Giving teachers guns will give guns to both good and bad people (some bad people are teachers!). That in particular is a horrible idea, I bet we'd go < 5 years before a teacher shoots a student. Just stupid.

The fact is, finding out who among us is evil is a battle that we've waged for all of human history. We get better at it and they get better at hiding among us. Evil people, undetected, can do evil with any policy on the graph. If society were to engage in a "moon shot" for advancing our ability to suss out the evil among us, an evil person would almost inevitably misclassify innocent people. It's a really tough problem, but we should probably keep at it.

Responding to the school shooting directly: Appeals to authorities were ignored. Are there enough spurious reports to authorities to justify this? School resource officers were hired to mitigate this situation after columbine, here that mitigation failed completely. Do they need more training, better access to intel? (IE: real time info on shooter movement inside schools, etc.)

Those kinds of questions might be asked, but it's all too easy to derail information gathering and honest discussion by tacking on Side1 or Side2's reactions to it with glue of "and that's why we need to".

What marks a good wedge issue is one where both sides blatantly ignore nuance, and whose solutions have broad collateral damage. The collatoral damage to each opinion should be abhorrent to the other side, and uncomfortable but ignorable to your side.

Another interesting thing that really flummoxes American society are gradients that get transformed into binary policy arguments. Arguments over abortion, healthcare, capital punishment, social security, welfare, civil rights and unions represent the neural network of human society trying to figure out "How much is a human life worth?"

The societal instinct is to say "priceless!" and smartly so, because to admit otherwise IMMEDIATELY creates very bizarre side effects. The abortion debate is basically arguing whether (m1 * mother > m2 * child). We try to argue about what m1 is and what m2 (life begins at ?!?!), and pretend that mother and child are both weighted to infinity.

Going to stop ranting before I accidentally write a book. Hopefully you found this interesting.