You need to be critical of these people calling for social bounty campaign, most of them won't invest into the project at all and even if you ask them what the project is all about they can't explain.
There are too many scammers in social bounty campaigns, you are right. It's not that difficult to create dozens or even hundreds of fake Twitter accounts, for example. Detecting and eliminating the cheaters is a difficult and expensive task. I can assume the social bounty campaign can be not profitable in this sense. ICO team should spend their tokens, their time and sometimes real money to handle the social bounty campaign. The above spends can outperform the possible social campaign results in terms of ICO investments.