Two thoughts spring to mind...
1. I hope you don't say that to anyone you run sound for, lest you bum them out and ruin their set.
2. I hope you don't try to impose your will on bands by doing things like refusing to run them a mic when they want one or insisting that they turn down so low that they can't even hear their amps onstage (don't laugh...I've had a handful of idiots try to do that).
Whether someone's rig is special enough or not to mic up really isn't your call. If a bass player thinks his rig is special enough to where it should be mic'ed up instead of DI'd, there's usually good reason for it. Maybe bass doesn't take the "traditional" role, or maybe they're going for a sound that desn't work with a DI. Or maybe they just plain like the sound of their amp mic'ed into a PA. It's not something that you can apply a one-size-fits-all solution and make blanket statements about.
If its a house sound guy, it usually pays to listen to him. After all, he knows the room and its quirks better than you.
A sound guy should let you run a mic no matter what, but if he wants a direct you should give him that too.
If you run sound all the time, you know how frustrating it can be when a complete tool insists on something and you have to compromise a nice clean mix to accomodate. (Like a bassist refusing to DI on request and not being able to bring him far enough up in the mix because of a poor job of him setting up his rig to perform correctly).
There are more 'complete tools' and 'tone freaks' out there that have no idea which way is up outside of their basement than there are ones that have a clue.
Running without an amp? Not in this lifetime, bro! I don't care what you say...I think it sounds like crap to have to listen to the bass in monitors, and sorry...what I listen to onstage is every bit as important as anything coming out of FOH.
Yeah, I'd never run without an amp. You could have a killer preamp and the most expensive DI box currently available and it is going to sound like poop 9/10 times through monitors (compared to a bass amp thumping beside you).
Few places invest much in stage monitors. You never know what someone is going to drop on them, be it small hard objects or beer.
Only exception I guess would be IEMs, but why would you want to subject your band mates to horrible stage monitor tone?