As a cis ally who also belongs to the LGBT community, I oppose bans on transgender athletes' participation because I know it's important to stand up for our community as a whole, even if I'm not 100% educated on all of the finer details.
What I mean by this is that I'm not a sports fan myself. I was never athletic in school, and my knowledge about K-12, college-level, and minor/major league professional athletics, in general, is quite rudimentary.
I love how you're speaking out as a transgender person who is also an athletics coach, and we need more people like you to circulate the necessary education (interpersonal plus written/archived, alike) from which more cisgender people can learn.
I want to see new generations of young people who identify as transgender be supported with the health care and community-based social structures needed to live authentically. The medical side of one's journey transitioning is also one where I need to become more informed, esp. as it relates to accessibility of medical services and resources.