Checked out the UK's immigration requirements recently?
Compared to getting a Green Card getting Permanent Leave to Remain is a major chore. The big hurdle is the family income requirement -- you have to earn about 20K (pounds) a year or you can't stay in the UK.
The 'public charge' thing has always been in US immigration law. As with any regulations its never 100% cut and dried but the general sense is well known -- to receive 'immigration benefits' you have to be a net contributor to US society. The thing you've got to watch with the Trumpenfanatics is that they're subtly moving the goalposts, redefining what being a public charge is and applying the rules retroactively.
Incidentally, I have relatives that have moved to various countries from the UK (and one that moved to the UK from El Salvador) so I'm familiar with the various hoops that you get to jump through to get residency status. The US is actually pretty easy; its main problem is that its grossly oversubscribed (although our removal of the welcome mat might fix that....). I should also mention that just because you turn up in a country doesn't make you an immigrant; unless you're got the appropriate documentation you are just an alien -- a foreigner -- residing in the country who may be in or out of status.