But primaries are about political parties choosing who should represent them aren't they? Political parties are private clubs. If you aren't a signed up member of that political party why is it any of your business to have a say in who represents them?

Why should private clubs be determining who is on the ballot?

If they had that role removed, they would still be able to endorse a candidate or agree to all vote for the same candidate or whatever.

I don't know much about US politics but I don't think they are determining who is on the ballot are they? They're determining who can claim to be the official Republican Party but I don't think there's any reasonable grounds to say that that's wrong.

Ted Cruz can still be on the ballot if he wants to can't he? As an independent? How could the Republican Party stop him?

There's "sore loser" laws in some states that would be a problem, and he would have to collect thousands of signatures in most states where he wants to be on the ballot.

It's a complicated morass of rules that would cost a lot of money:

https://ballotpedia.org/Filing_deadlines_and_signature_requi...

In contrast, the parties essentially have a reserved nationwide slot that they fill after many months of media circus.

"Why should private clubs be determining who is on the ballot?"

They don't. They pick two of the people on the ballot. Anyone has the chance of getting on the ballot if they aren't part of one of those groups.

"It shouldn't matter if a Democrat is voting Republican or the other way around. People can change their minds, and should not be disallowed to vote if they find that the other party is doing a better job in making the country a better place."

This is the Primary. Not the actual election. Those people are free to vote for whoever they want in the general election.

"If a whole bunch of Republicans vote Democrat, it means that the Republicans have failed to do their job!"

In the general election, yes. Not in the primary. In the primary, it means that one party is trying to choose the candidate in the other party that would be easier for their party to beat.

" Saying you can't vote because of that is like a childish loser saying you can't play for the opposing team."

No, it isn't. Not when you realize what election you're talking about.

"My point is that such a decision should not be made and it segregates our democracy and makes it an "us vs them" fight, when in reality we're all in this together."

Your point doesn't make sense when a party is trying to pick it's own candidate.