[GeeTwo]

The policy that no one can be excluded from a team is certainly peculiar. Does the football team have the same policy, really? Anyone who doesn't show up, or shows up and doesn't dress out, or doesn't do the drills gets to stay on the team?

One of the first things we did once our team got larger than about 30 members was to create the "varsity" vs "junior varsity" distinction. The bottom line was that varsity members got to take the "field trip" to competition on Thursday and Friday. This provided a good bit of incentive for those on the fence.

This year, when we had more than about 50 applicants (our build space is a biology classroom, and 50 is packed, especially when it's cold out and the grinding moves indoors), we implemented a tryout system. Selections were made primarily on attitude, not aptitude. This helps ensure that even those people who still have a long way to go to contribute aren't serving as a distraction. The attitude of our team this year was massively improved from previous years.

Even if you can't actually exclude members from the team, make as many things as you can dependent on real participation. This includes varsity (field trip), "lettering" in robotics, and any other recognitions you can think of, such as designation as an officer (looks great on a college application) and so forth. While it's certainly not the best way to go about this, you may be down to implementing "constructive termination", in which you encourage those who participate and call out those who do not to such an extent that they quit.