Overturn laws that limit auto manufacturers from selling their vehicles directly

In cases such as Wikard v Filburn and Raich v Gonzalez, the Supreme Court has held that Comgresses power to regulate extends to any activity which, in the aggregate, substantially effects interstate commerce. Such a test is trivially met by state laws forbidding the sale of automobiles directly from manufacturers to the public.

As bradleyjg points out, the Supreme Court copy of the constitution doesn't seem to include the tenth amendment. Between the commerce clause and the 14th amendment Congress can do pretty much whatever it wants.

Have you read the Constitution?

Here is the 10th amendment.

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.

If you read Article 1, Section 8, clause 3 you will find the Commerce Clause that grants Congress the following power.

To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;

When a manufacturer is in one state, and a customer is in another, the power to regulate business transactions between the two is clearly given to Congress by that clause. The 10th does not take that away. Therefore Congress should have power to regulate that commerce in any Constitutional way it wants.

(Note, your suggestion of selling liquor goes the wrong way. The 21st amendment expressly gives state laws supremacy in that case. But if no liquor is involved, then Congress should have authority.)

I am not a lawyer, but my lay understanding is that in this case the interpretation of the courts fits my reading of the text.

Limit it to the actions of doing nothing, of clicking/signing a petition, and writing a representative.

So, the question is if the likelihood of someone writing a representative is increased or decreased by the presence of an opportunity to click/sign a petition.

Sounds like the hypothesis here is that the satisfaction of signing a petition would reduce the odds of writing a representative, more than increase it. I could see it the other way though - maybe the civic engagement of caring enough to sign a petition would make it more likely that they'd contact a representative than they would have otherwise.

I wonder how the experiment could be structured? Maybe an educational/awareness web page, with a second step of an opportunity to contact a representative, while inserting the "sign-a-petition?" step in between?

There are some ecommerce people that believe that by giving buyers more-and-smaller steps to click through, it increases conversion, so who knows.

Frankly, I hear so much of this "oh that'll never do anything and it just makes people disillusioned" nonsense about ALL levels of engagement ("protesters are hurting their own cause!" "it's just a staffer who reads your letter!" "no one cares what you say!") that I'm extremely skeptical of all such claims.

Maybe rather than tell people who engage that they're failing it would be more useful to encourage them to succeed more.