Because you know someone who's LGBTQA*. Several, in fact. You're probably related to some of them, for that matter.
Because the right to life, liberty and the pursuit of happiness is not meant to be restricted to the privileged. Yes, we know how badly that was implemented in the late 18th century. But we owe it to the very idea to keep improving on it.
Because you are in no position to nominate someone for exclusion. None of us is.
Because it's a no-brainer.