Agreed, but posts based PURELY on referral advertisements are not okay. Let's look at an example:
https://steemit.com/bitcoin/@babarkhudai/100-instant-payment

It's obviously a scam and the steemian is only advertising it because of the referral link he added to it. That's what I meant with the referral link advertisers.

And I completely agree that it's okay to add a referral link to a valuable post, but there's only a small percentage of these scam advertisement posts that's actually valuable. Most of them are pure referral link advertisements, like the one above.