One of the common mechanisms that homeschooling parents use is a co-op mechanism. A group of homeschooling families in an area decide to school their children together, with varying degrees of cohesion. This, especially coupled with extracurricular activities, can easily address any concerns about socialization. The adults I know who were homeschooled and seem to have socialization issues by and large were homeschooled in a bubble and not encouraged or given opportunities to socialize. Another benefit of these co-ops is that they can allow for shared resources and expertise that replicates some of the other benefits of a more traditional school environment.

An easy example of this might be to take advantage of guided tours of theatres or museums. It's not often easy to get a guide for one parent and one child, but organizations will accommodate a group of 30 more frequently. Another example of this collaboration is electives. Even the best-intentioned homeschooling parent might not know some skill their children have taken an interest in (e.g. cartooning), but if another homeschooling parent knows that skill (e.g. a professional cartoonist), it's common for such parents to make arrangements for lessons in the interest of the group. A parent with an interesting hobby (e.g. model rocketry or electronics) could very easily expose other children to that hobby in an educational way. A group of willing parents can go a long way towards replicating the breadth of educational experience that a traditional school and its resources can provide, without any of the drawbacks.