To start with.
Smartcasting and Autocasting are 2 seperate things.
Autocasting is where a unit will use an ability or spell, without the players input.
Smartcasting is where if a spell is ordered to a group of units, only 1 will follow out that order instead of the whole group.
Smartcasting seems to be flying under the radar underneath the massive MBS argument, however I know there are mixed opinions about smartcasting, and I think that if blizzard is reading these forums, they should know our stance on the subject.
Now I can see why blizzard would implement smartcasting, it is an easier way of controlling your spellcasting units and maximising their efficiency. However there are drawbacks that come with the system that I would rather did not exist in starcraft 2.
Skill - Ok, well this is pretty straight forward. It takes more skill to effectively control your spellcasters if there is no smartcasting. Less skill means less areas for a player to prove that he is better than another. It lowers the skill gap which is bad for competition.
Requires weakening of spellcasters - In starcraft, spells were major game changers. Spells such as Psi Storm, or Irradiate were feared by zerg due to the ability to the sheer damage that they were able to inflict on your forces. What limited this damage from being overpowered was the relative difficulty to use a spellcaster effectively.
Smartcasting seeks to change this, making the use of spellcasters much easier. If spellcasters are easier to use, then their relative strength will have to be diminished so they are not overpowered. This can be done in a number of ways:
Spellcasters can be made more expensive,
their spells can be made more mana costly,
the effects of the spells could be diminished
With the first two methods, the downside would be spellcasters losing part of their role as an investment unit. Currently spellcasters are something you buy, with the potential of being worth much more than what you paid for them.
While this isnt too bad, it's the third option which would be really bad for the game, and what it looks like blizzard would be implementing.
The final option is to weaken the spells themselves. If youve seen from the gameplay pics and vids, Psi storm might be getting a much smaller radius. Simply this is boring. Spellcasters are supposed to be devestating units, not just another part of the army. This was a major problem I had in warcraft 3, where there was very little that could do mass damage to units. By weakening spells, you make the game more boring for players and spectators alike. People want to see 20 units get wiped out by a single spell. There is a reason why the korean commentators scream "HIIIGHHH TEMMMPULARRRR, PSSSIIII STOOOOORM". Its because these high powered units have the ability to change the game soo much with just 1 spell. I would hate to lose this in exchange for an easier casting system.
Logic - This point isnt as big, but it still is valid. When you order a group of marines to stim, they all do it. When you order a group of ghosts to move, they all do it. Why should only 1 use lockdown when you order a group to do it?
Rewards players for grouping - Blizzard has announced that the unit selection in SC2 will be about 150. By not implementing smartcasting, you reward people who use individual groups rather than the easier 1 group army. You are rewarding people who have greater control, and will help to keep the skill gap wide in starcraft 2.
These are my views so far. Please discuss yours.