.... Any groups speaking in defense of or in favor of metal detecting ? We need to have a voice in the laws that affect us.
Yes. That is what the FMDAC was formed for in the early to mid 1980s-ish. But their hands are largely tied. Because un-like the NRA or something with scores of hobbyists, md'ing is a geeky niche small hobby. Un-likely to raise up the type funds to buy lobbyists, lawyers, etc... Just too few in our ranks for that kind of finances.
And actually, the more we (groups like the FMDAC) go to bat to "make a stink" and "fight", it actually often only works to back-fire and bring about more laws against us

In other words: sometimes the LESS visibility is better, not the MORE. Because we are in a hobby that has admitted connotations . That you might be about to (gasp) find something old. Or that you might be about to "remove" something. Or that you might about to "dig", etc.... And the less those things occur to people , the better. Yes I know that's a "catch-22", but ....... just sayin' .......
..... I have been to another state park in the area and employs there saw me, waved and never said anything. .....
So too has this humorous same thing happened to many others. They simply had "no idea". And ironically went for even up to years, with nothing but a friendly wave. No one ever said so much as "boo" to them, and it was painfully obvious no one cared.
Imagine their surprise later, when someone on an md'ing forum (or club meeting or whatever) tells them "isn't that place off-limits?". Hmmm, So you tell me, since it's become painfully clear that no one at said-location cares less, what do you do? Give up your honey-hole ? Go "alert those rangers who previously never cared so they look it up in their dry dusty minutia and tell you 'no' " ? (and then start booting others?)