...seems to be immediately invalidting my opinion about the subject, which is effectively denying me a voice.
No, that´s not how having a voice in the discussion works. You state your opinions, preferably followed up with some arguments so people can see what you base your opinions on. Then others chip in, they might agree or they might not, but if they do not agree, or even (oh the horror) happen to think something you said was stupid, that is not denying you your opinion or your ability to voice it. That is nothing more than disagreeing with your opinion. Regardless what you happen to think about anything under the sun, someone is going to disagree.
I reccomend you learn to deal with it, because not being able to handle this part of a discussion will indeeed make people not think very much of your opinions.
