Sorry. "Everything is unfair, so we don't need to try" is just sloppy reasoning.
We do try. We have multiple age groups and multiple levels. We have boys leagues, girls leagues, adult leagues, and corporate leagues.
The question is not whether we try to divide people into different groups in order to create fairer games. The answer to that question is clearly yes.
The question is, given that we divide kids into different groups, what is the correct group for a teenage boy experiencing gender issues.
You are correct "everything is unfair, so we don't need to try" is sloppy reasoning. So is "we have to preserve a level playing field" because there is no such thing. The only thing we can do is create lines which hopefully are rational (and therefore justifiable) and therefore not arbitrary. Like borders on the map, though, they are an artificial fiction, and someone is going to get screwed.
It's also not rational to say the trans person (whatever their natural sex or chromosomal makeup) should be the one to get screwed just because of who they are. That's just bigotry. Someone is going to get screwed in this situation, the only question is who.
So, you think performance is an issue, you better be focused on performance. It's not rational to say we don't care about the cheaters (who are also using testosterone) but we do care about the trans kid. Also the trans kids whose performance is not impacted (mtfs on puberty blockers or surgery before puberty, ftms not on hormones) should be allowed to play in the female division. Girls who are caught up with unusually high testosterone need to be dealt with too.
If you think it's safety, you better be worried about the 5ft kid who is facing the 6ft and not just care about the trans kid.
If you think it's genetics (which is really a purity test), you darn well better not exempt the genetic anomalies and if you are going to test, test everyone.
The biggest question, though, is always what difference does it make. As far as ENCL kiddie soccer is concerned, at least to date we haven't shown a whole lot of concern in the 3 categories of issues that have been raised. The moral hysteria around trans kids is therefore not justified. It may very well be in other areas such as single sports or college D1 sports.