Even though true (free trade sounds good in concept), the answer is not that simple nor is free trade actually that free. China subsidizes a lot of their industries and also bans US companies from setting up shop directly in China. Musk is a big supporter of China and when Covid happened, he didn't say a peep about their lockdowns, but was very vocal in the US. He has also stated Taiwan should just go back to China which puts nearly every US industry at risk due to chips alone (memory chips come out of Samsung/SK Hynix/TSMC). As mentioned earlier, Nvidia manufactures everything out of TSMC.
China subsidies (note scmp is owned by Alibaba):
China’s industrial subsidies have long been a lightning rod for Western criticism of “unfair” trade practises, but Beijing says the issue is being used to block the country’s development.
www.scmp.com
This stretches to oil/gas/food pretty much any industry so it's easy to be against tariffs, but China has tariffs on US imports as well actually (during Trump years so it's not a Dem/Rep thing).
Musk needs China more than China needs Musk IMO so his mouthpiece typically echos what China wants so it's a biased opinion.
Outside of this, I'm not sure it's a good long term thing for US society to flood the markets with cheap imports. There are societal risks with job losses, crime uptick, a lot of undesirable outcomes.
To save multiple posts, looks like MY production is cut in China?
Tesla Cuts Model Y Production in China, Report Says. Competition Is Raging.