The French tend to prefer the sound "a" to the sound "i".
This is why they use "là" to mean "here" and "là-bas" to mean "there".
By the same token, they prefer "voilà" to "voici", "cela/ça" to "ceci", etc.
So are they really interchangeable unless you want to contrast 'here' or 'this one here' with 'there'?
I wrote "I'm not here to argue about that", and I feel that's more natural English.
The back-translation would not get back to the French sentence/verb/meaning:
To argue = débattre/discuter/argumenter
Could it also mean: "I am not there to challenge that," as if the person would challenge if he could but he is not physically there?
"Contester" = to challenge, contest, dispute (v). As noted by Sitesurf, here is one of the many situations where "là" is used for "here". Look for the natural translation which is faithful to the French (in which là also means "here").
But what is wrong with "ça" instead of "cela" (Je ne suis pas là pour contester ça)
"Ça" is also fine in that sentence. It's just the informal way of saying "cela".
Yes, but I wouldn't have written that if it had not been rejected. A cry of protest.