Because Super PACs can't coordinate with candidates, sometimes the PAC will end up hurting the candidate more than helping them, by presenting a different message than what the candidate hopes to present. And in my professional blogging opinion, this election cycle showed that no matter how much Super PAC money you have, you can still lose badly if you are not a good campaigner and a good fundraiser, independent of Super PAC funds. And if you don't believe me, look at Jeb Bush (tons of Super PAC money, terrible campaigner) or Scott Walker (tons of Super PAC money, couldn't raise enough campaign cash to continue to pay his staffers).
Are Super PACs a problem? Yes, because citizens deserve to know who is donating to what campaign, and there should be limits on how much people can donate. But is a well-funded Super PAC necessary to win an election? Absolutely not, and grassroots organizing of people can and has overcome money in politics. And reforms are possible to reign in Super PACs and fix campaign financing, so don't give up hope! But if you need to calm down after learning about Super PACs, you really should watch the McConnelling Daily Show segment. It's truly a work of art.