I've been lifting for a few years now and I really dislike the cargo cult mentality when it comes to heavy lifts, mainly barbell deadlift and squats. If you're not trying to become an olympic lifter, barbell squats and deadlifts will do more harm than good. There is a significant chance of injury if you perform these lifts improperly, and it's hard to know when you're doing them right. There are good alternatives to each (goblet/dumbbell split squats) which are safer.
Well, there is a basic risk/reward here. If you just do arm curls working one muscle group and you'll be pretty safe but you won't be getting much return on your overall physical health. The deadlift involves your whole body and so you are increasing your surface area or exposure to risk of injury. But that was the whole point of recommending the deadlift in the first place, it works the whole body with one basic movement. And the movement is one of the most basic human movements, to squat down and stand up with a load. There are risky exercises that you should generally avoid. But standing up with a barbell in your hands is a well designed exercise where your body is just doing what it is optimally designed to do. The problem isn't the movement it is ignorance about the body in general and your body's movement in particular.
I think a compromise to your point (e.g. safer alternatives are better than deadlifting) is that advice to do heavy barbell lifts should come with the warning that injury can happen easily and be serious and/or permanent. Proper posture is best learned from someone who is experienced and that you trust your well being to.
"If you're not trying to become an olympic lifter, barbell squats and deadlifts will do more harm than good."
Sorry, but this is utter insanity. The squat and the deadlift, properly performed, are the most important lifts _any_ human being – young or old, male or female – can do. And a person _does not_ need to go heavy on either of these to realize tremendous benefits in their day-to-day life. Spending 6 weeks to get up to a 135x5x1 deadlift (bar + big plates for 1 set of 5 reps) – and then just doing that once a week in perpetuity – would be single most efficient way the average human could improve their daily wellbeing.
I do understand where you're coming from though. We often times see guys at the gym quarter squatting or pulling with a rounded back which is indeed doing more harm than good.
anecdotal counterpoint :) -- squatting aggrevates my lower back. I think its because my hamstring flexibility is terrible which causes my squat form to be terrible. I'm working on that.
I also have flexibility issues (I'm tall), and I used to strain my lower back on heavy squats until I widened my stance and pointed my toes a bit more outwards, to prevent my lower back from rounding. You could ask someone to check if your lower back arches towards of the downwards movement.
Anecdotal data point: my lower back pain disappears when I squat regularly.