True, tbh. Losing LP isn't enough because they'll get carried in 40% of the games anyway; there needs to be something extra for these fellas.
It's a problem when they refuse to communicate with the team at all. When their fed laner roams and ruins everyone else's KDA (hiding who really is the intentional feeder), or when they refuse to go in with our jungler to ruin his chances, it's taking the effect of his own play and putting it over everyone else's head.
The sad thing is that people get banned etc for flaming (which is good) more often than intentional feeders get banned for doing what they do.
A simple solution is to give people time-outs of 5, 15, 30 minutes if they're on a losing streak where they themselves are the reason for the losing. Another would be just to remove those people from ranked altogether.