Why not? We allow pretty much everything else. Appliances, consumer electronics, car parts, batteries, etc.

The one and only reason to not allow Chinese cars is to try and protect domestic auto industry, but considering how expensive and mismanaged domestic auto production is I don't see that as a good excuse. They won't die because they can't possibly compete, they will die for refusing to compete because they want higher profit margins now rather than bulk sales and good public perception 10 years down the line. They would rather fuck their future and bet on a bail-out than dare try making bulk cheap cars again with a bit lower margin.

Hell GM paid Toyota to come teach them how to make cars cheaper and better and build matrix platform cars in their factory. And what did they do when that happened and cars started rolling off the line? They complained that Toyota didn't produce them them in the same manner they would have, and then closed the plant down. Meanwhile Matrix platform cars like the Vibe are highly sought after on the used car market because they were known for reliability and ease of maintenance.

If we were actually worried about security, we would be doing FAR more than merely disallowing HuaWei products. Its like living next to an active volcano in a forest fire prone areas inside a log cabin and then screaming about how dangerous it would be to allow matches be sold in stores due to arsonists.