You do realize that if they wanted to cause mass destruction they already have nukes.

The defense from weapons of mass destruction is the same no matter the type, it's retaliation. China could build an ion cannon on the fucking moon and the threat would not be significantly larger than a nuclear weapon, because if they used their death ray the US would retaliate with nukes.

Humans already have the technology to render our planet devoid of life. A new weapon of mass destruction is not some dramatic leap in lethality, because you can't get extra dead.

For that matter, China is already extremely reluctant to have WMD. They maintain only 100 300 nukes to dissuade other countries' nuclear aggression, even though they are much much richer than Russia and could easily afford thousands. They also have a standing policy of No First Use, which is a commitment to allowing their enemy to nuke China first, before they retaliate with subs. They do this because they never want nuclear escalation and so the USA won't see a malfunctioning launch detector and immediately assume a nuclear strike.

oh no what if china gets a weapon whatever will we do, they've never had weapons before!

Yes but almost all SPS designs are microwave. If you use laser then you get blocked by clouds. A 2GW microwave transmitter in geostationary will give a footprint of several square miles. Birds could fly through the beam without harm.

Assuming you're using a phased-array transmitter, which is the only practical method, the only way to get even that much focus is to use a reference signal from the ground target.