It’s the law.
The Americans with Disabilities Act is Federal law, and you run the risk of a messy and expensive lawsuit if you’re in violation (or even accused of being in violation). How much of the ADA applies to your group or event may vary, but this isn’t something you want to find out the hard way. If you have liability insurance, if you have a 501c3 tax status, if you have a group large enough to need written rules, you should consider your accessibility policy and actions.
It’s welcoming.
Your community prides itself on being inclusive, accepting, and welcoming to everyone, and that should include those with either visible or invisible disabilities. The positive word of mouth that an accessibility program will generate will pay itself back with more attendees, more good will in the fandom and in the community at large, and more growth for the event. An accessibility initiative also demonstrates good will in other areas of diversity, inclusivity, and equity. If your group states that it’s welcoming to all creeds or to the LGBTO community, or has resources specifically for persons of color, or any other similar outreach – then you need to consider disability. Intersectionality exists, and there are disabled people in all subgroups.
It’s easy.
Making sure your events and programs are accessible isn’t difficult. Someone from the disability community, or a trained accessibility volunteer, can do a lot to make your event more welcoming and accessible without a great deal of extra labor.
It’s affordable.
Many groups mistakenly assume that ADA compliance or providing accessibility is too expensive for a small organization. The ADA has an exemption for groups to not provide expensive services under the “undue burden” clause. However, there are many things you can do that are extremely affordable—even free—which can display your group’s good intentions towards the disability community.