In answer to your question, you won't ruin your clutch by not using it, but you are more likely to do damage to your transmission by not using the clutch. That doesn't mean you will damage a gear, but the odds are increased. I try to always use my clutch. Clutch plates are cheap and simple to replace. Transmission parts, not so easy and not so cheap.
With the exception of racing or serious race practice, I really can't see why anyone can't use their clutch on almost every shift. It's so imbedded in me after many years of riding, I have to consciously not use the clutch.
Still, there are plenty of riders that seldom use their clutch with little if any ill effects.