"Bad for you" is a phrase I generally reserve for things like a hot cup of strychnine or chili that's been left out at room temperature overnight. Food--even processed food--is unlikely to be downright
awful for you as your friend claims, although it might not be the absolute best choice nutritionally speaking.
But nutrition is only part of why we eat. We also eat for taste, convenience, variety, habit, and half a dozen other considerations. A Lean Cuisine meal that isn't the best nutritional choice may give you the ideal combination of low calories, convenience, flavor, and variety that'll let you stay on your plan. If that's the case, then it's absolutely fine.
I eat them occasionally myself, but as others have mentioned, I don't find them very filling even though I like the convenience. To make up for that, I generally eat them with a sizeable vegetable side dish. They make a chicken artichoke panini that is remarkably tasty, but at 300-ish calories, it's pretty small; round it out with a salad or some sauteed snow peas and you'll push it to 350-400 calories or so, but you'll be plenty full and will have a better nutritional balance in your meal.
They are high in sodium too, but if you aren't salt-sensitive, that shouldn't affect your overall health (though it could cause bloating).