Because you have no response to being told to look at historical context. Look at post 11. I'm sure the President of the Constitutional Convention thought the 1st Amendment was about being allowed to cuss your brains out. And definitely not about avoiding prison or death for criticizing government. You know, like in England.
"Is, then, the Federal Government, it will be asked, destitute of every authority for restraining the licentiousness of the press, and for shielding itself against the libellous attacks which may be made on those who administer it?
The Constitution alone can answer this question. If no such power be expressly delegated, and if it be not both necessary and proper to carry into execution an express power--above all, if it be expressly forbidden, by a declaratory amendment to the Constitution--the answer must be, that the Federal Government is destitute of all such authority."
James Madison, Report on the Virginia Resolutions; Jan. 1800
http://press-pubs.uchicago.edu/founders/documents/amendI_speechs24.html
There's no doubt the primary purpose of the First Amendment is to protect people who wish to criticize the Government.
But limiting it to that - which the Founding Fathers explicitly did not do but could have in plain language - would mean the Government could punish me for (among many other things):
* Telling people who to vote for
* Circulating petitions & soliciting signatures
* Any/all of the books I read, movies I watch & Internet sites I visit
* Contributing to certain political candidates, parties & organizations
Are you prepared to say the First Amendment does not - and was never meant to - protect the above?