Trouble is, there's a lot of baggage underlying this issue. For a long time, teachers and schools were subjected to an ethos that claimed that spag was irrelevant, old-fashioned, boring, not to be taught. So there are a lot of adults around whose skills in this area are poor. And we are quite possibly looking at a shortage of headteachers very soon, because of the increasing (and often contradictory) pressures they are being put under.
Not only that, this ethos still lingers. There are still people in education who disagree with the idea that spelling etc are important, and who, crucially, think it is wrong to judge or assess children or adults on it. Some of those people have considerable influence.
Worst of all, the people who judge schools for failing to produce good spag results (Ofsted) may well then, as individual inspectors, criticize those teachers who use the most effective methods for teaching it, on the grounds that these are not sufficiently child-centred. So teachers essentially can't win.
All of this contributes toward the somewhat fraught attitude to criticism we've seen here.