Lightside Darkside is an absolute moral system.
The game's system to represent it is anything but that.
I find a group of Storm Troopers hassling a street vendor demanding bribes or they will arrest them. So I try to talk them out of it with influence enhanced charm check I get yay 4 dark side pips. So my I'm trying to be a light side paragon good guy just went out the window, because my dice roll just turned dark not because of any decision I made, but random chance. Random chance is not an absolute morality its random. (Its actually got a 60% chance of coming up dark side so its not even that random). I don't have the successes with out those dark side pips so my I'm trying to be a hero moment was jacked by random chance into me going all darkside, not because I wanted to, but the dice gods demanded it. How is that a good system?
Mean while other character goes screw this and straight up kills them. Takes confict and at the end of the night rolls a 10 while I roll a 1 well **** it. Other dude is rewarded for darkside, but me I just dumped down further on the darkside tree. Not because I wanted to, but because random dice gods were not with me tonight. How is it that this is any less worse then straight up assigning conflict based on actions?
In the scenario given here, it could be easily role-played that in that instance, your PC was so stressed out and worried that they drew on those darker emotions, not being quite at peace with themselves and the Force as they'd like to be. Unless you're a player that's completely lacking in imagination, it's quite simple to narrate why your PC earned Conflict in such situations; while the player themselves may not be sweating bullets about directly confronting a bunch of stormtroopers, the character is probably worried, and likely considering all sorts of "worst case" scenarios should their mind trick gambit fail, or worse backfire hard enough that the stormtroopers turn their attention to the character.
If you watch the "Shroud of Darkness" episode of Rebels, Yoda pretty much confirms that the struggle for a Jedi (and extension any other Force user) to not let their fears and doubts consume them is a life-long struggle that never ends. Yoda even admits to Ezra that he, as wise and knowledgeable Jedi Master that he is, faces the same struggle as Ezra does.
As Kael pointed out, the system is designed so that Conflict isn't anywhere nearly as harsh of a penalty as Dark Side Points were in prior system. The designers have even outright said that it's expected that PCs will earn a few points of Conflict each session simply from using those dark side pips to occasionally fuel their Force powers.
To say nothing of your own BS about how going for directly attacking a bunch of stormtroopers in that instant would be the "better solution" simply because it's less Conflict generated, simply for how narrow of a view you're taking on the situation. Unless the GM is a lazy prig that's not doing their job properly, blatantly attacking a group of stormtroopers isn't going to be as quick and clean as using a mind trick, and is invariably going to have consequences beyond earning Conflict. Using the mind trick averts both immediate violence and likely later violence down the road as nobody's going to be looking for who just butchered a group of stormtroopers; as a GM with that scenario, I'd say the troopers have an open comm line to their HQ and will have the opportunity to call in that somebody is attacking them at their current location. And if the PC attacks with such overwhelming force as to slaughter those stormtroopers in one attack, then that's going to be more than 1 Conflict at my table, possibly 3 or more, to say nothing of the consequences of directly attacking and butchering those stormtroopers in front of eyewitnesses.
Also do remember that the Conflict table is called out as "suggested guidelines" much as the chart in the combat chapter about how to spend Advantage/Triumph/Threat/Despair is called out as "suggested guidelines." In both cases, the GM is advised to make their own decisions, be it how much Advantage/Threat is needed for a particularly secondary result of a skill check, or how much Conflict should be generated for certain actions.
While Star Wars as a setting has an absolute morality, the Conflict/Morality system is set up in such a way that not all crimes are 100% equal, and that the GM can have some leeway. Murder is still murder, but as a GM I'd assign a hell of a lot more than the standard 10 if a PC randomly butchered an innocent child that hadn't done anything to deserve that fate than I would if a PC beheaded a defeated adversary that had been trying to kill them but was no longer an active threat.