[Arios]

The Sorceror's is natural and innate, while the Wizard's is a mimicry to produce the desired effects, but not "natural" as much as constructed, carefully measured and timed.

EDIT: This is another reason why Sorcerers might be looked down upon, they are upstart and don't really know what power they have, and not wise enough to wield it safely since they were never schooled in it. At least that is what one might think.

Expanding on that last point, sorcerors can and should be seen as extremley reckless and massively dangerous as they increase in power. The big difference is while a wizard spends years of hard training and patient discipline aquiring say, a fireball, a sorceror can be down the local tavern in a heated arguement, snap, and suddenly channel all that anger into a fireball, reducing a fair portion of the place and the people in it to ashes and kindling.
They're really not someone you want to be letting run around unchecked.

And a big thing right here! Wizards use and have high intelligence for spellcasting whereas sorcerors do things via charisma, so, force of personality.
So, a sorceror who can cast the gate spell is unlikely to stop and think "Wait a minute, is unleashing a balor on the streets of Bezantur really a good idea?", and more likely to think "Eat that guy that tried to mug me!"
And then the balor goes on a rampage, fireballs and implosions fly, buildings are destroyed and people maimed. The balor is happy, the local authorities are not (assuming they wern't killed).

Essentially sorcerors are (generally) magical hotheads that burn down their enemies, allies and all the structures inbetween, especially when provoked to anger. Not really the type of people you want running around unchecked.
Whilst wizards are (generally) the calculating types that burn down only what they intend to burn down.

Sorcerors = collateral damage.

Lots of collateral damage.