Allow me to summarize what it means when a company wants to handle all disputes in arbitration:
No matter what they do (delete your data, privacy breach, overcharging, whatever), you don’t get to sue. Instead, THEY get to choose the arbitrator according to whatever criteria they want, and thus any dispute is decided by someone they’re paying.
Also, you can’t join a class-action suit against them.
Like the writer, I love Dropbox but I’m also recommending you go do this right now.