I am giving someone a gift tomorrow and I really need to use a tool to finish it. Can I join and finish my project this afternoon?
Short answer: no.
Long answer: Every single time we've tried this, it's ended with a ruined project and everybody frustrated. We simply cannot sign up, onboard, and train every member who walks in the door, help them with their project, and also expect to get anything else done.
That's why we've moved to scheduled orientations and tool training sessions; it's a much more effective use of everybody's time, and it lets our staff and volunteers plan ahead to accommodate the needs of the community.