We know for a fact that the US is doing everything they claim that Huawei might be doing. The NSA monitors communications on a mass scale. The US routinely hacks into the communications infrastructure of Europe to spy on senior European politicians. The US NSA has direct access to major data links which connect data centres in the US, giving them access to unencrypted data stored there, and they do take advantage of it. US networking hardware gets equipped with backdoors in a targetted fashion. Under US law, American companies must hand over any data they have access to to the US security services on demand, and they can be imprisoned if they tell anyone about it. This has all been in the news over the past few years and so isn't in dispute.
Should the rest of the world therefore ban all US networking equipment and US companies from anything related to communications or critical IT systems? I mean if you are going to be consistent, then that is pretty much where your argument leads.
Meanwhile the US has declared Canada to be a "national security threat" because Canadian steel and aluminium might do something bad to the US. They also say that Germany is a "national security threat" because German cars might suddenly start goose stepping down American streets when Angela Merkel presses a button on her desk.
And now the US president has recently announced that he wants US industry to lead the world in 5G technology. I think it's pretty clear how the US determines what constitutes a "national security threat". It's called mercantilism, and it dominates US policy making these days.
Most of the rest of the world seems to be saying "thanks but no thanks", as they don't see any reason for making themselves poorer in order to bail out American companies who have fallen behind in the technology race.
If there is a genuine argument to be made for security in telecommunications hardware, then it is an argument which says that each country should only being installing kit made within their own borders by companies controlled by their own citizens and monitored closely by their own security services acting under the control of their own parliaments. Perhaps that doesn't sound like the best of ideas, but it's exactly where this anti-Huawei argument leads for those willing to be honest and consistent about it.