I've talked about this issue before, I happened to just now catch it in the act and had to share. Here's the video of this thread
As you can see, over a thousand comments with a variation of 5-10 different compliments about the exchange in question and 99% upvotes meaning barely anyone has downvoted it or there are way too many upvotes. Someone who doesn't check past the first few will probably go ahead and sign up to the exchange, maybe use the same email he uses for other exchanges and maybe even the same password (get password managers, people, it's important) and boom, some of you might have your funds stolen on the other exchanges you use the same credentials on.
Reddit has unfortunately become too mainstream, and since the community is not self-regulating in the same way as it is here on Steem where spammers either run out of bandwidth quick or face consequences of getting downvoted and not being able to pretend to be good guys later again or get to delete their past history. Not only that but on Reddit you can't see voting activity, which account voted what and which account downvoted what which here is made crystal clear through the blockchain.
Since Reddit is mainstream and gets a lot of attention, that means accounts receive value as there are black markets with demand to buy the accounts for malicious activity or advertisement. The activity of accounts that goes on on the Reddit database can only be viewed by an admin, so moderators and regular users will just have to guess what is going on. In this case it is of course quite easy to determine that this is all a paid advert and you can see how many accounts these guys have bought or paid to compliment the service. Imagine though the ones that aren't as cheap and obvious as these ones, they are probably advertising something to you right now if you are browsing Reddit without you knowing. As long as something can grab your attention, it will have value.
I am not saying that these things will be completely impossible on Steem, but everything being open-source and tools being possible to scan people's voting behavior and determine which accounts are acting "weird" it will be a lot easier to get rid of these manipulations and false advertisements.
I didn't even get into the whole dangers of what a centralized database such as Reddit can do unfairly to you and to your freedom of speech, that I can bring up another time and a lot more downsides about it.
