The hold isn't anything uncommon. They claim that it is a security feature, and has happened to many first time buyers (pretty sure there was a thread a while back regarding the same issue), but I feel like that they are really lacking in terms of communicating clearly with the user BEFORE they deposit any funds that there will be a security hold.
Otherwise, it's no different an exchange holding up your withdrawal, at the expense of the user. You don't know where your funds are being used, heck, it could be used to fill the liquidity gap in their operations for all you know.
I would strongly suggest you move away from using Coinbase, but not from trading bitcoin entirely. Don't let this one negative experience with a specific firm known for shitty customer service and constant holds/account suspensions drive you away from the wider market. Despite the worse rates, using P2P exchanges gives you a heck of a better experience overall, so you should consider that at well.
I second this for sure.