Some guys, especially those who like to define themselves as "hardcore" or "a serious lifter," have an irrational hatred of the Smith machine. Most women are either in favor of it or indifferent to it. And many top male bodybuilders love it. Even some strong-as-hell powerlifters use it for certain accessory lifts.
But there are a ton of guys who are outraged that the Smith machine even takes up space in the gym. And the arguments against it usually come back to, "It removes the stabilizing muscles involved in the barbell equivalent movement."
But what if that's the whole point? What if you need to train around an injury that you're rehabbing and the Smith machine allows you to get in a position you can't get in with a barbell? With a Smith machine, you could still train pain-free and stimulate muscle growth.
But if your ego is so huge that you can't be seen in a Smith machine, then you're only hurting yourself. And that degree of insecurity is what makes you a little bitch.
Oh look, here's powerlifting master coach Dave Tate using a Smith machine, but you're more hardcore than him, right?
What if you have levers that make certain barbell movements inefficient at building certain musculature, and the Smith machine enables you to hypertrophy that area? Dorian Yates was a thinking-man's bodybuilder, and he found that Smith machine squats were superior than barbell squats for his body type. He did okay as a bodybuilder.
Need another example? Zydrunas Savickas has done well as a strongman competitor and routinely uses the Smith machine to build his overhead press.
Labeling the Smith machine "worthless" is like labeling all of Canada worthless because they gave us Nickelback and Justin Bieber. Okay, those are pretty good reasons, but you get the idea.
Now, if you're ONLY using the Smith machine, then yes, your stabilizers won't get the same degree of work that they'd get with a barbell. But most people don't just do Smith machine work, either. Most people who approach training with even an ounce of intelligence use a variety of movements – with and without machines.
The Smith machine, like almost everything in the gym, is neither good nor bad. It's how you apply it for your goals that ultimately makes it a good or bad choice in your training.