Learn Hardcore Russian: Это всё равно не повод спорить.

Это is a neutral pointer meaning this/that. In this sentence it refers to the situation you just mentioned (the reason, excuse, or circumstance already understood from context). Starting with Это is very common in Russian to introduce a judgment: This isn’t a reason to…, That’s not a повод to….

What does всё равно mean in this sentence—anyway, still, or it doesn’t matter?

All three are close, and context decides the best English rendering. Всё равно literally suggests all the same and is used for:

anyway / in any case: It’s still not a reason to argue.
still (despite what was said): Even so, it’s not a reason to argue.
it doesn’t matter (less literal here, but possible): Either way, it’s not a reason to argue.

Why is не повод used instead of something like не причина?

Повод is more like a pretext / excuse / occasion (a “trigger” people might use to justify an action). Причина is a more neutral cause/reason.
So не повод спорить often implies: Even if it’s true, it’s not a good enough excuse to start arguing.

What grammatical form is спорить here, and what does it imply?

Спорить is an infinitive. The structure (не) повод + infinitive means (not) a reason/occasion to do something.
So не повод спорить = not a reason to argue.

Could it also be said as Это всё равно не повод для спора or …для того, чтобы спорить? What’s the difference?

Yes, both are natural:

не повод спорить (infinitive) = direct and conversational.
не повод для спора = focuses on the noun a dispute/argument as an event.
не повод для того, чтобы спорить = more explicit and a bit heavier/more formal; often used when you want to sound very clear or emphatic.

Is the word order flexible? For example, Это не повод спорить всё равно?

Russian word order is flexible, but it changes emphasis.

Это всё равно не повод спорить. = Even so / anyway, it’s not a reason to argue. (emphasis on “regardless”)
Это не повод спорить. = neutral statement.
Это не повод спорить всё равно. sounds marked and usually needs special context; it can sound like you’re tacking on всё равно as an afterthought.

What’s the tone—does it sound polite, firm, annoyed?

By default it’s firm but not rude: you’re shutting down escalation. Intonation decides a lot:

Calm, falling intonation: reasonable boundary-setting.
Sharper stress on не повод: can sound impatient (That’s no reason to argue.).

Does спорить mean a friendly debate or a heated argument?

Спорить can mean both:

to argue/disagree (often heated)
to debate (can be calmer) If you want clearly hostile “fight/quarrel,” Russian often uses ссориться. If you want “debate” more academically, дискутировать is common.

How do you pronounce the tricky parts, especially всё and the stresses?

Key points:

всё contains ё, so it’s pronounced vsyo (not vse).
Stress: всё (single syllable), равно́, по́вод, спо́рить.

Could this sentence be shortened or made more informal?

Common variants:

Это не повод спорить. (simpler, still natural)
Всё равно не повод спорить. (drops это when context is obvious)
Даже так — не повод спорить. (means even so, slightly more expressive)