> as they definitely work harder for less pay and rights than the local poor.

Why would I want to support the introduction in my country of what is virtually modern slave labor practices by abusing and exploiting the poor and desperate foreigners so that some business can get richer because they don't want to pay or provide decent working conditions or invest into automation?

Especially that a lot of those cheap laborers without rights aren't even doing work to the benefit of the community (elderly care, construction etc) but to the benefit of a few wealthy and unscrupulous business owners (Amazon, Uber Eats, etc) who are addicted to cheap exploitable labor.

>Countries may not like foreign poor immigrants, but they certainly need them to work harder for less pay and rights.

Yeah, but there a major differences in which these are implemented that can make immigration a success or a failure.

Some countries that you also mentioned like Middle East, Hong Kong, but also Singapore import those workers for cheap labor so they can do the work the locals don't want and in exchange migrants make money to send back home, making it mutually beneficial, but they don't get the right to permanently settle there or gain citizenship because they don't want them as citizens, they just want temporary workers that will work and then leave when they're no longer useful or wanted.

This however does not apply to most western nations where migrants can settle permanently and relatively easily become citizens with voting rights in a relatively short timeframe(at least in EU), and that's where the anxiety of the locals comes from and also their hatred of migrants. They're importing an alien culture they're not fond of as cheap labor, that once settled and granted voting rights, if not integrated properly and harboring animosity, can demographically displace them via their higher fertility rates(natives are already minorities in some major EU cities) managing to out-vote them and force their culture onto them democratically, or worse, use their majority status to take revenge for how their ancestors being treated as cheap labor. Either way, this is a recipe for endless racial tensions or even conflicts in the future, that isn't being priced in to the economic upsides of mass migration which only looks at GDP.