Some conservatives are against tariffs imposed by the US. But true conservatives are against all tariffs, including those imposed against the US. Unfortunately, even Reagan fell short in this area (as he did on immigration and some other issues). He was a great president, but not perfect. Thankfully, Trump is against all tariffs and realizes that reciprocal tariffs are the only way to create leverage and eventually negotiate foreign tariffs (and subsidies, etc.) away.
I agree, that we should oppose protectionism, which is the imposing tariffs that are not reciprocal and for the sole purpose of creating an unfair advantage over another country. But I also oppose pretentiousness, which is pretending that the tariffs and subsidies imposed on us don't exist.