It's not stealing from China to not give them something taken from someone else.
UK could have demanded a lease renewal from PRC as the price for switching recognition. Instead they just got some “alliance” against the Soviets and it is questionable what that actually delivered.
Giving HK back to China is an act of decolonization. Putting them under Taiwan and loading up the island with US weapons would not be.
PRC is itself a colonialist power. See all the Uighurs in concentration camps.
I don't want to devalue your experience, but Anglo powers have a terrible record of "colonialism for their own good", "we'll be greeted as liberators", etc.
China doesn't like to take credit for that, but personally I believe its alliance with the West was instrumental in the collapse of the Soviet Union.
You really want to set the precedent that regime change voids all international agreements, rather than obligations and rights under them passing to successor regimes?
And I spoke that after having of talk with a Japanese people today and they fear they are the next on the list. I told them Japan at like 6th or 5th powerful army despite Article 9, + US alliance (that we all understand as half trustable only), so quite able to defend themselves. A lot of people in East Asian (HK, Vietnam, Philipines, Japan) fear China. This is what I got from talking with friends from this country. Everyone think there will be war at some point, only the time and starting place is unknown.