I think it should depend on the circumstances. I can accept that parents are to some extent responsible, but there comes a point where they will have to head off to work. For my parents, my Mum was often able to come with us as far as the bus stop, and sometimes even saw us get on the bus, but she couldn't really see us all the way to the school gates without being late for work herself (although she has flexitime hours, which makes "late" something of a loose concept, perhaps). Dad meanwhile had to go to work earlier than we had to go to school, or at least wasn't really able to take us into work without inconveniencing his own start to the day.
This could be a counterproductive policy, in particular if, in trying to avoid the child being late for school, the parents ended up having to be late for their own jobs. If it's demonstrably the case that it actually is the parents' fault (because, say, they're dropping the child off late), then fine -- but in many cases I doubt it would be fair at all.