Unfortunately, there is a whole segment of backpackers who give 'backpackers' a bad name. It is for this reason that the word 'backpacker' is a derogatory term in many places. When an initially good idea like Couchsurfing comes along it starts to become known through word of mouth to a group of like minded people.
Take WWOOFing for example. Initially, it was intended to allow people from cities in the UK to go out to a farm for a weekend and learn about organic food. The original name was Weekend Workers On Organic Farms, thus WWOOF. The intent was for the worker to gain some insight/knowledge and hopefully when they returned to the city they would start buying orgainic farm produce which would be a benefit to the farmer.
But over time, WWOOF has changed dramatically. First, it has become a business that sells memberships. Second it is no longer only about organic farming, just about any kind of company can join WWOOF and look for part time labour in exchange for room and board. In other words, using the participant.
On the other side, many people now join only to get room and board for a few hours work and see themselves as getting more out of it than the farmer/business. In other words, they are using it for selfish reasons. So now both sides are trying to get the best of the other.
Obviously, not all participants are like this but it is inevitable given human nature that this is what will happen. Couchsurfing is no exception. From an initial idea of a cultural exchange where the traveller met and spent some time with a host, it has become something that is posted about here and elsewhere as a 'free bed' for a traveller. As a result, someone may show up at 6pm looking for a free meal, spend a couple of tours telling their host what a savvy and worldly traveller they are, go to bed and leave in the morning, but not before a free breakfast.
If you Google you will find information and people who believe anyone who says they don't Couchsurf primarily for a free bed but primarily for the cultural exchange are kidding themselves (to put it politely). You will also find that Couchsurfing as an organization has become controversial and its practices questionable indeed. Again, the money making motive comes into play. So you get questions about 'where does the donation money go' and various other allegations of impropriety.