Usually the price goes up quickly and then down again to where it came from within minutes - it does not lose it´s original value. Not sure really how that can harm a coin, and also I don´t see why people would lose faith in cryptocurrencies because of that. I assume that who sees cryptocurrencies in a serious way completely ignores the pumps and dumps. They´re there for players and cowboys, and not for long term investors who don´t need to really care about them.
I still miss to see anybody explaining what´s harmful to crypto coins about the pumping. It looks like empty propaganda with as little value in it as the many pump groups with extreme promises that make no sense. But just like sportsbetting is only harmful for the fool who puts all his saving on a bad bet, but not for the sport itself, cryptopumps are not harmful for the cryptomarket, just for whoever decides to gamble with all that he´s got.