FA is good, insofar as the bullying and stigmatization of overweight people is a major social problem that needs to be dealt with. I do get a bit frustrated when blogs like TITP try to claim that big people are being outright oppressed, going so far as to compare not being able to fit into amusement park rides to racial privilege, or when members of the FA community engage in blatant hypocrisy ("real men like meat, not bones!") but the core message -- that a person's worth as a human being isn't connected to their weight -- is a good one.
HAES is... eh. If it were simply a matter of viewing health as a complex picture, rather than a single stat (BMI), I'd be fine with it, but outright denying the link between obesity and any number of health problems -- as a very large segment of HAES does -- is not only unscientific, it also puts lives in danger. The movement is chalk full of claims that people have genetic set points of 300+lbs, that BMI (or even blood pressure, cholesterol, and blood sugar, in extreme cases) is 100% useless when determining risk factors, that metabolic disorders can somehow magically defeat the laws of thermodynamics... I just can't be okay with something that's so full of misinformation, especially when it's a matter of public health.