The problem in not the 100x itself but rather the opportunity which it creates with a practically anonymous account. I say 'practically' because even if someone is giving his name, his actions are not monitored like on regulated US exchanges.

Take the numerous cases in which CFTC discovered derivate manipulations. What does this mean? Simply speaking this means that one person (or family, or a circle of friends) sells simultaneously on spot market and derivate market taking advantage of its own action. With regulated exchanges it is easier to find these people and to sue them for their illegal actions. Many of us were suspicious about the CME gaps for example, expecting a dump to fill those gaps at $9600. Well, it happened several times before but not this time, which shows that CFTC is working well with CME. 

On the other hand, it is much easier with a 100x margin to manipulate the marked by selling both on mex and some less liquid spot exchange. There is a risk of a price swing of course, but theoretically such practically anonymous persons or entities could do this endlessly. If there is no monitoring on behalf of mex staff, then everything is allowed. And this is by no means good for the natural growth of Bitcoin. Not to mention that there are numerous suspicions that mex owners are playing against their clients. Of course, they know all their positions and can squeeze them anytime. I can recall for at least 2 articles in coindesk and cointelegraph about it. They also can turn off the server in case something goes wrong like 12 March crash. And finally, I really don't believe that the owners are innocent and not cooperating with money launderers. So, the hodlers should have no tears or remorse for mex.