The security of a wallet depends on the user, if the user knows how to protect its wallet from attacks and hacking attempts it is 100% secure.
Exactly, if a user use the exact myetherwallet website then the person will not be loser. But if the person use any malicious site or fake site where the person enter private key then the person will loss everything as fake site can store that private key.
That's why it is always good to check the website before accessing the wallets and sometimes it is not good to open outside from your laptop because by chance you might click other fake address which they will steal your private key.
Usually people too lazy to type web address on site. And then they trapped in phising site that appear in google search. Well, actually it is risk that they must take. Because if we type it manually, we can confirm web address that we want to visit.
Lazyness do really leads out to loss of money.We know that phishing websites are just lurking on the net where targeting mostly wallets or exchangers which those scammers
do know on where the honeypot is.Users safety would always rely or depend on its own hands,if you are sensible about security then proper research would be crucial.