Australia also doesn't have an illegal immigration problem on the same scale as the USA. You're also ignoring the symbolism which will serve to discourage illegal immigrants and drug trafficking.
You said drugs was one of the reasons they built the wall. That's what my argument was mentioning australia. We don't share a border and get drugs here easily. No reason to think building a wall (fence lol) stops drugs getting in (also as a pointed out drugs are not the reason they are building it anyway)
If 2 border walls/fences are built for the same reasons why is one xenophobic but the other not?
You are trying to fix the argument by stating in the question they were built for the same reasons.
Trump promised to build a wall not because it was the right thing to do , but because it was the popular thing to do. It's a promise that earned him the votes of many Americans and it was predicated on the xenophobic reasons I've already been through.
How is that different to Mexico building a partial fence on a South American border that is used by cartels to smuggle weapons in? Did the Mexican president use it as a ploy to gain votes from xenophobic conservatives so he could rise to power?
As much as you wanna stand by trump and whatever you think he will achieve you can't ignore the link between conservatives and xenophobia and pandering to that group. Go ask anyone why gay people can't marry in America , and who fought against equal rights for people of different race. A large section of xenophobic conservatives. Trump rose to power exactly because he promised what these people wanted to hear. To deny any different would be as obviously wrong as pretending the moon doesn't exist. the wall (fence) is being built to please a bunch xenophobes. The only purpose it will ever serve is getting trump elected and that will be about it.