Coinbase also charge fees for transferring from money-to-money, usually for deposits of USD/GBP/EUR and withdraws (once the user exceeds $1 million).
There are also peope that believe that Coinbase are tracking people's identities.
I think any tracking has to do with KYC and staying out of money laundering. It's been a while but I have seen coinbase take action if you are suspected of selling on LBC. SO there is somesort of tracking for them to stay legal how much no one really knows.
I don't know if I agree on forums it's a discount. Normally forums and LBC cost more to buy BTC then Coinbase. They are normally cheaper to what I have seen.
Some sites like bitbargain.co.uk are usually cheaper than Coinbase. I know that is is not USD but it counts for the same.
Mostly, people try to get away with using Bitcoin on The Dark Web, so tracking in this way may not be a good thing for some users.
Though, prosecuting people for illegal activity is a good way of controlling Bitcoin and also to stop it from falling into the hands of extremist organisations.