Gox isn't unprofessional because they made a mistake. Everyone makes mistakes. They are unprofessional because of their pathetic and disgusting attempts at damage control, which involved trying to deflect blame to the entire world other than themselves.
Mt Gox is unable or unwilling to act proactively since 2011.
They don't fix issues before they turn into real problems - they only take action after those issues have escalated into a catastrophe. Then, to add insult to injury, they barely talk to their customers at all and what little information they do release is incomplete and typically raises more questions than answers.
What do we know about Mt Gox's wallet problems?
1. It doesn't know the difference between newly-minted coins which can not be spent for 100 blocks and old coins which can be immediately withdrawn, so sometimes is credits customers for deposits which can not actually be withdrawn and it sometimes also attempts to include unmatured inputs into outgoing transactions.
2. It has a habit of producing invalid signatures, which it did not correct last year after the network started rejecting transactions with invalid signatures.
3. 1 and 2 combined to create a situation where a certain percentage of all withdrawals would end up "stuck" and never confirm. Instead of fixing the two root causes of this situation, they instead created a permanent workaround in the form of reissuing withdrawals. Maybe this was intended to be temporary, but it turned into just a normal part of doing business.
4. Their method for reissuing stuck transactions was sloppy in that the new did not invalidate the old one therefore it was theoretically possible for both transactions to be included in a block (customer gets paid twice).
5. Their wallet did not continually reconcile the blockchain against their internal accounting. If one of the inputs they believed was unspent got consumed by a transaction that was included in a block other than a transaction they were expecting, their wallet would not notice this. Presumably this happened because it only checked the blockchain for what it was expecting to see.
6. Because of the previous 5 mistakes, transaction malleability made it possible for malicious customers to trick Mt Gox's internal accounting system and pay them twice (or more).
So naturally they blame the Bitcoin protocol.