KEYS.

Now that ends up for the users themselves to make it secure. Sometimes, being scammed is mostly the user's fault and not the wallet or platform itself. An internal breach can happen anytime even with the most protected and secured wallet and that's the only time we can blame the wallet.

Overall, using MEW is "safe" but it doesn't mean users need to rely solely on it.

https://notyourkeys.org/ - This subject is for BTC but the idea can be applied in general.