It will bring harm to them because they are the one that decided to sell their bitcoins. Because they think that their profit is already enough but they are the ones that are giving some doubts about bitcoin's pump. Instead of making bitcoin pump, when they are doing panic selling they are not helping anymore.
But if the price of bitcoins exceeds their entry price and if its giving them huge profits then I don't think its smart to hold their coins at that stage and instead they should be sold to get huge profits from it as if you will never sell your coins then you will never make profits from it.
Profit is profit and there are traders that are doing it as long as they had their expected price. Just like me, I'm doing this sometimes but for only the small portion of my bitcoins. It's suggested that when you have the right profit already don't have doubts on selling it but the wrong thing is that most of us are doing panic selling when we are seeing the price to fall.
The reason behind panic selling is that people lack patience and they get panic when they see price going down and start selling their coins at cheaper price and I think that is the time when we should hold our coins tight and wait for the price to bounce back again but generally people doesn't follow this simple rule.
Yes patience is being gone to those holders specifically long time holders. But for traders, as long as they are having enough profit, they are not doubting their move for selling their coins. I just experienced the disadvantage of being a panic seller. Because you surely will regret this move upon seeing the price to pump.
After knowing bitcoins since long time we cannot afford to repeat the same mistake again and again by selling our coins at lower price when price starts falling even I have made the same mistake in past when I was new to bitcoins but now I will prefer to hold them even if price dumps.