The older I get, the more amazing it is to me how people can have such strong opinions about things they know little or nothing about.
We home educate. We don't unschool but know many families who do and without exception their children are bright, motivated and enthusiastic with numerous talents and interests, many of which they've persued to a high level. I know several who are now adults and have had no problem going onto further education or employment.
The law says you must provide a 'suitable' education and defines that as 'that which equips the learner for life in the community of which they are a member'. How you achieve that is largely upto you. Home educators don't have to teach in a formal way, follow the national curriculum or take exams if they don't wish to, but It's worth noting that most families DO take GCSEs and/or go into further education, and that includes many unschoolers. If an unschooled child wants to follow a career path which requires certain qualifications, why wouldn't they be motivated to study for those exams? Unschooling isn't about avoiding anything which looks like traditional schooling.
Unschooling isn't about doing nothing or just letting the child decide what they want to learn and expecting them to magically come up with a schoolish answer like the romans or trigonometry. A HUGE part of unschooling is creating a rich life (in terms of education and experiences, not money), about introducing children to new information, ideas, topics, concepts, opportunities, but with the focus on helping the child finding their talents and their passions.
The unschooled children I know have a range of interests, some which look nothing like school and many which do. One is about to take GCSE history at age 10, another is passionate about languages and is fluent in several, both from following their interests and passions. Persuing an interest may well involve hiring tutors or seeking out mentors, again it is NOT about avoiding anything which looks like formal schooling.
As for reading, it's common for home educated children, even when not being unschooled, to learn to read at a later age, often around 8 or 9. Schoolchildren would too, except everything in school requires being able to read, so we teach children intensively to get them reading as soon as possible. Home educated children, taught one to one and able to go at their own pace, don't have that urgency. Of the research I have seen and going also by personal experience, home educated children who learn to read at 8 or 9 have caught up and often overtaken their schooled peers within a year or two. Unschoolers DO help their children learn to read if that child wishes to be helped, but yes, some children do learn without formal teaching. We live in a literate world where almost everything requires being able to read and write, so children are naturally motivated to want to be able to read and parents are on hand to facilitate that. The idea that left to their own devices a child will choose not to learn to read is nonsense. Barring one with severe SEN and one with dyslexia (who is receiving help) I dont know any home educated children above age 10 who can't read.