If we are simply looking at products that “might be harmful” to people, then it is beyond question ethical to market them to people.  The product that you give as an example (cars) is clearly dangerous, but it is also extremely beneficial to huge numbers of people.   We surely cannot ban the marketing of products that are very useful simply because they “might” harm some people.

If you think about it, practically any product that you care to name could harm someone.  I could cut my hand with a knife in my kitchen.  I could drop my vacuum cleaner and break my foot.  I could swallow a piece of meat wrong, choke, and die.  The world is not a place in which we are guaranteed to be safe.

Because there is an inherent risk in being alive, companies need to be allowed to market products that could harm us.  The products that they market will generally give us benefits that far outweigh the possible harm that can come from them.  If we were talking about products that have no benefit and can only harm people, then marketing would be unethical.  But such products wouldn’t sell anyway since no one would want them.

Since every product out there can potentially harm people, it is impossible to say that we should prevent the marketing of products that “might be harmful” to people.