Good question and the point of discussion. Most user don't care about settings or ads as long as their usual activity is not impaired.
What does the ISP gain with it ? I think most people won't notice. I'm more worried about the step back regarding net neutrality of this ISP.
Some people suggest that this filtering is a move in the long fight the ISP has with google to get it to pay a share of the network usage cost.
While the ISP is very user friendly, for net neutrality and open minded, Google and more specifically Youtube, is a totally abnormal situation. Google earns billions in advertisment and don't give a cent to ISP while the traffic of Youtube is largely dominant on networks.
One move the ISP did in the last years is to reduce Youtube traffic bandwidth and claimed the problem was due to a network peering issue. More and more people complained of the problem so that the ISP had probably something to do about it.
It is thus suggested that the ISP might be targetting the revenue source of Google without impairing user experience.
The thing is that Google has probably pushed the shared network usage model beyond its reasoable limit. It kind of make sense to me that the network infrastructure cost should be sharde between producers and consumers. This usually tends to naturally balance and even itself. But with Youtube and Google there is a very strong imbalance regarding network usage and profit making.
If other ISP would make a similar move, this could initiate discussion to find a fair solution.
I doubt The ISP would try to cut revenue of reasonable free web services living from ad revenue, because this is its bread and butter.
Except, the bandwidth has already been paid for, at least twice.
Once by the consumer by way of a monthly internet bill and once by the content provider(website) in the way of their hosting/bandwidth costs.
It is not clear by the ISP's name(Free) whether or how much they are charging for internet access. negrit seems to suggest that this ISP has a fairly aggressive pricing model.
However, if the cost of people actually using their internet access, especially just to browse websites, is too much for Free, they should look to their pricing model or consider upgrading their networks, as opposed to trying to extort(or at least block) advertisers.
As you mention, this ends up being a much bigger issue in regards to net neutrality. For now, it is just youtube that is using 'too much' bandwidth, but blocking that will only mean other sites will take its place as bandwidth hogs.
Hopefully this will result in discussions to finding a fairer solution, but I believe that should involve upgrading infrastructure and providing better service, rather than blocking sites like youtube or netflix.
Here is a french blog post providing more information on this explanation which, according to this post, was indirectly confirmed by Xavier Niel, the founder of the ISP.
