I believe you must follow the leaders if google has it on his than why give away those links from your site. I have probably 300 gambeling sites abored with great pr.
Can't be any worse for the Google trust issue than linking to a multitude of industries verses sticking to one theme . . . (recalling a Matt Cutts post about a site linking to multiple non-related industries).
Hard to say... i saw directory with regular sites and also porn sites... and they don't have any problems with Google. Good positions and so on.... Yeah, and some sites suffer for just 1 bad link.
Maybe you can use "nofollow" tag and offer casinos sites only traffic withaout link SE value.