I appreciate your question, Really Goin' Nuts (Your mother definitely has an imaginative mind to have named you that -- Is she a writer, too?  But don't you get ribbed a lot for your middle name, "Goin'"?)  Your situation is a common one since, as the famous saying goes:  "Those that hold the purse strings do not always know what the hell they're talking about."  (Actually, it's not that famous of a saying since I just made it up, but it could be if somebody had made it up earlier, like way back in historical times when people really cared about what people said and wrote it down for posterity).  I agree, R.G.N.  It can be very frustrating to know what's best for your script and have to defer to those who are in charge of it and think they know better than you do.  My overall advice is to go ahead and go nuts.  Or really go nuts.  Hey, isn't it amazing?  That's also your name!  Will wonders never cease?!  What I'm referring to is to be real with your feelings, and if "nuts" is on the day's menu, then, by all means, order them.  Let yourself feel your initial reaction.  I'm not saying go nuts forever, to dwell in any feeling or obsessive thoughts (unless you're obsessing about finding the home address of the producer in question because you're planning on picketing his place all by yourself and brandishing a placard that reads:  "I'm Not Really A Stalker Because I'm Holding Up A Sign."   I've heard that can work.)  

The point I'm trying to get across is that you have to be honest about how you feel.  You're a writer, an artist, and your feelings about your work are very valid.  You want to honor them.  But the key here is to not let your feelings dictate your actions.  (I underline the previous words because I have very strong feelings about them being very important.  Although, that may change in the next five minutes and I may feel strongly that I shouldn't have underlined them.  Thank God and the Holy word processor.)  If you and many screenwriters in a similar situation did that, I'm not sure there would be all that many lovely films to watch.  Because so many of those screenwriters would have quit and walked away from their projects.  So, then, studios would have to bring in scab writers, who would have to cross the walk-away-from-the-project screenwriters' picket lines.  And where would that leave us screenwriters?  It would leave us struggling to answer a very important question:  "Do I picket the producer at his home or at the studio?"  Not an easy one to face, don't you agree?  Not to say that you can't go ahead and up and quit (I never did figure out what "up" had to do with quitting.)  Quitting is very dramatic and whose to say that as you huff out the studio offices, a wandering producer won't spot you immediately and say, "Say, you look like a talented screenwriter who has been woefully wronged.  Would you like a six-figure deal to write my memoirs?"  I'm not saying that couldn't happen.  But, just in case your Mercury might be in retrograde (or Pluto conjunct with Goofy) or you're not assured of your next screenwriting job, you might want to consider another option, regardless of how your feelings are adamantly wanting you to self-righteously make a stand and tell that producer that you will not allow him to degrade your inner artist and that he can go straight to hell:  that place where producers go and are made to bring breakfast every morning to their screenwriter masters.

So, if you don't quit, what to do?  It begins with making a choice.  Or reaffirming an original one.  Did you decide to see this project through?  And are you still committed to that choice?  It's essential at this juncture to look at the big picture.  What's waiting for you at the end of this rainbow, as slippery or steep or just plain not as colorful as you want it?  Monetarily speaking, is there more possible treasure waiting there?  Do have any backend agreements?  Points?  Rewrite money if and when your screenplay sells?  Career-wise, is a credit waiting for you, and possibly a gateway into WGA if you haven't been there yet?  You see, there's always a bigger picture.  Will you gain more confidence or ability to collaborate?  (not a bad idea since "collaborate" seems to be one of the main verbs you need to master to ascend the ladder of screenwriting success.  At least it sounds better than "compromise," don't you think?)  There can be many payoffs to do your very best to see your original project through, even though there are far too many hands (or just one "stupid" one) in it for your satisfaction.  But that's a major key:  Your satisfaction is not the concern of everybody else involved with your screenplay.  They're too busy singing their own version of "I Can't Get No... Satis-fact-ion."  You have to take care of your own satisfaction.  You have to live with you on this and many more projects that will come up in your future.  And you want to be able to handle a similar circumstance with less trouble and use your experience you gained from a previous one to see you through it with much more ease and success.

Here's some pointers that have helped me, personally, to get through difficulties when others in power want to tamper with my screenplays:

1.  Don't let them and send them to Producers' Hell.

Just kidding.

1. Be honest with your feelings.

2. Re-clarify your goals with the project.  Remember to look at the big picture.

3. Prepare and know your script forwards and backwards (although be careful about the "backwards" part or you'll end up writing "Fade Out" at the top of the first page) so that you can offer the most astute and incisive suggestions in order to guide the producer to accept your writing as is.

4. Don't overlook the possibility that the producer might have some effective, and -- yes, I've got say it -- better ideas than particular ones of yours.

5.  Give as much room to the producer as you can.  Remember:  Producers like to contribute.  Many of them are wannabe writers.  Heck, some of them are writers.

6.  Look forward to the possibility and marvel of synthesis, that your fantastic script could actually be enhanced and you could have a better chance for a major success  because of the collaborative efforts of others. 

I know that these concepts may be a bit foreign to that right brain and creative part of you, the same part that is a genuine genius when it comes to imagining and writing a wonderful screenplay.  But you need to let your left brain in on the project, the reasoning, analytical aspect of you.  Hey, why don't the two of you do a lunch and see what you can come up with?!

Just don't let Lefty push you around.  If he does... just walk out on him.

DcH