Is there fate?
Nope. Although our minds are conditioned to react in a certain way, and our behaviors are programmed to tend toward certain actions. For this reason alone it is better to be more conscious and have more choice, to respond rather than to react.
If so, are we fated to be the bad evil slave?
There is no reason to see this parable of Jesus' as anything other than a brief teaching tool, it should not be thought of as prophetic or conflated into some kind of archtypes that apply to "classes" of people. The WTS abandoned trying to turn all of Jesus' parables into prophecies decades ago, they should have tossed this last one aside as well.
If the bible prophecies that there will be an 'evil slave that falls away and beats his fellow slaves because the master is delaying'...
(except there are no Bible propheicies that say this)
...doesn't that mean that someone has to fulfill that prophecy otherwise the prophecy would be false?
It's not a prophecy.
In other words, some one or a group of people have no choice but to be the 'evil slave'. Just like it was prophesied that someone would betray Jesus... so no matter what, one of the apostles had to betray him... they couldn't just all have chosen to be loyal.
There is much speculation regarding Judas' motivations, and schools of thought that cast Judas into various spiritual or political roles.
Jesus, regardless of motivations, needed a mechanism to get himself into Rome's hands. In this way, Judas is acting under Jesus' direction and can in no way be "fated to betray" anyone.
Couldn't it be that most every one on earth doesn't have a choice but to reject God because if it were any other way prophecy wouldn't be fulfilled?
Then certainly we are all only always doing God's will and we need to get over our petty judgments whether we are blessed or damned - we are all merely pawns in God's game, doing His will at all times with no right to judge our own actions or anyone else's.
Is it our fate to be the bad one?
Nope.
Do most people have no choice but be bad because of all the prophecies, that were made before they were even born, said they'd be bad? (Broad road to destruction, etc, etc)
Nope. In that mode of thinking, we are characterless, empty vessels of God's will, always doing what He needs. Again, we would have no impact on ourselves, therefore no right to judge ourselves.
I'm just thinking because I've always known from childhood that I would be the bad one... I wanted to be the good one but I wasn't. I always felt like Cain...
That's your over-active mind judging you.
We are often "assigned" roles in our family of origin, and most family members unwittingly conspire to enforce those roles.
This may sound rude, but it's time for you to individuate away from your family's expectations (which you have taken on as "true" about yourself) and realize you have choices, you have identity outside of your relationships with your family, and have the opportunity to create your life as you wish it.
Didn't Jesus say that it would have been better if Judas had never been born?
...and then Jesus went right on serving his disciples, including Judas, so it couldn't have been the grand pronouncement of damnation you seem to see.
Doesn't that mean that some are destined for destruction regardless of what they want?
You can make up what it means any way you want, but the end of this line of reasoning is that we ALL can only do what God has forced upon us, so there's no point in worrying about it.
The other possibility is that it's all a load of tripe, and you can (with a little effort) choose the kind of person you want to be.