What's the problem with renegade mages?

One of the questions asked by one player was why the Orders of High Sorcery were so Inquisition-like when interacting with other wizards.

You can then tell them the stories: Before high sorcery, magic was wild/chaotic, and wizards casting spells did sometimes critical mistakes, resulting into tremendous damage.

But if the player then replies: "I want to make a vanilla-wizard. No High Sorcery moon shenanigans."

To be fair, in the rules, there's nothing to justify the background/historical explanation, and the wizards of High Sorcery then appear like overzealous, intolerant morons.

Here, I propose a modification in the D&D5 rules to explain why mages of High Sorcery are not that crazed.

Non-High Sorcery Mages in Krynn

Important: My campaign happens just after the Chronicles/Legends novels, so the only arcane spellcaster class is the PHB wizard. This might change later, of course. But this is the state, and has been the state since the foundation of High Sorcery.

Wild Mage in Krynn

So, any wizard who was not trained by a suitable tutor (i.e. someone with sufficient High Sorcery education) is considered, in rule terms, as a Wild Mage.

They are PHB vanilla wizards, in everything (rules, etc.), but unlike mages of High Sorcery, they are plagued with an effect called Wild Surge.

In rule terms, these Wild Mages can be converted to High Sorcery wizards of the same level, if given the right education/instruction.

Wild Surge

The rule is simple: Every time a Wild Mage cast a spell (or a cantrip), they must cast a d100. If the roll is equal or higher to 100 minus the (slot) level of the spell, then the casting is considered a critical failure, and a wild surge happens.

A wild surge is a chaotic, unexpected effect, replacing the expected spell effect. To determine which wild effect happens, use the AD&D 2nd Edition Wild Surge Results table, which can be found here: https://adnd2e.fandom.com/wiki/TOM_Wild_Magic_Tables

Keep in mind this is treated like a critical failure: In other words, it is expected the effect will be altered in such way by the game master as to maximize unexpected damage. For example, one effect might enhance the power of your magic missile spell, like launching 50 magic missiles instead of a mere 5. But these magic missiles would fire at random targets, including other party members, friends, or even simple passerby civilians.

Also, I would even go further, and replace the entry for result 96 with: Spell effectiveness (range, duration, area of effect, damage, etc.) is multiplied by 100. This makes very clear un rule term how a Wild Mage is a danger to everyone anywhere near them, no matter how well-intentioned they are.

Innate Mage in Krynn

Some mortals have a natural, innate talent for magic.

For example, the mother of Raistlin and Caramon Majere was prone to some kind of fugue ("she let the magic control her").

In rule-terms, they might be handled as D&D5 sorcerers, but with the same Wild Surge rule above applied to them, no matter their sorcerous origin, possibly with a variant table focusing on their background (for example, the mother of Raistlin might have had a table focused on different kind of psychosis-style effects.

As above, these Wild Mages can be converted to High Sorcery wizards of the same level, if given the right education/instruction.

What about other spell casters?

This is handled in the same spirit as above. Anyone practicing arcane magic without a formal High Sorcery training will be subject to wild surges.

Divine Spellcasters

Their magic coming from gods and goddesses, they are not subject to Wild Surges, of course.

In my campaign, rangers, druids, and even bards are considered divine spell casters.

Former High Sorcery mages

Mages who left the orders can (and will usually be) considered renegades.

Those who continue to study magic while dodging the Test are always considered renegades.

Those who passed the Test successfully, but for some reason have diverged too much from the guiding principles of High Sorcery are also considered renegades.

But as they have the training of a High Sorcery mage, they are not subject to Wild Surges.

Conclusion

Now, you have a tangible reason to justify the existence of the Orders of High Sorcery.

You might find the rule impractical, or unbalanced against players who would be attracted by the idea of playing a Wild Mage, but this is the point: You don't want to use the rule in gameplay.

This rule is there just to explain in objective terms why mages of High Sorcery are wary of any non-High Sorcery wizard.