I am all for stopping any and all discrimination but the only way that can happen is to disband religions who are the major sponsors of such discrimination and that just isn't going to happen anytime soon.
Given that they, like many other US based conservative christian groups, believe that homosexuality is a 'sin' then they are free to have their own rules about it ... and suffer the consequences of people leaving as a result (shouldn't we welcome them making crazy rules that will drive people away?). They also believe in modest dress, especially when people are acting as their representatives on their ministry. Is that really, genuinely such a big deal?
Dress it up however you want (pun intended) the fact remains that this is an issue only to people who are actively digging to find an issue to be critical about. To most JWs it's simply common sense and part of their beliefs and to any 3rd party they will think you are nuts because religious groups having modesty-dress rules seems perfectly reasonable and normal.
If any argument relies on being compared to covering up child abuse to be "wrong" then I think that is a weak argument. Asking people to write neatly would be a crime ... when they don't report child abuse. Telling people to make sure their vehicle is well maintained would be a crime ... when they don't report child abuse. Resorting to comparison with child abuse to condemn any policy is rather weak. The real thing to focus on is things like their failure to report child abuse.
This sort of thing also gives them something to point to when someone raises a genuinely serious issue and a convenient get-out excuse:
"Well, you've been listening to those haters - look, they even have a go at us for suggesting our young folk should wear modest clothing. They go round looking for issues and making up issues that don't even exist, they invent things ... see"
I think there is plenty of serious issues to nail them to the stake for without trying to invent lame things that need to tie together multiple issues to be explained why it's wrong.
And when people start posting images of people in tight pants as has happened umpteen times then it really makes their point for them - they are immodest and out of place for a christian preaching setting.
Also BTW, saying that gay people can be identified by their clothing shows an ignorance and willingness to accept caricature stereotypes - gay people don't dress 24x7 like they are in a San Francisco gay-pride parade. They don't all shop are Gays-r-us ...