"Why don't conservative activists use SEC Rule 14a-8 (the so-called shareholder proposal rule) to put proposals on corporate proxy statements?" and speculates that to the extent conservatives do submit such proposals, they are likely to be excluded as ordinary business matters.

Well, I don't know if this represents a new trend or anything, but at least one conservative group was recently successful under 14a-8.  The National Center for Public Policy Research submitted a proposal to have Deere & Co provide a yearly report to stockholders on whether its political spending was in line with the company's stated values.  According to the proposal, Deere & Co has stated that it advocates for a free marketplace, and that it only supports candidates who share its "pro-business" outlook and commitment to "free enterprise," but at the same time, it has joined the Climate Action Partnership, withdrawn its support for the conservative ALEC, and has donated to politicians who voted for the Affordable Care Act and Dodd-Frank.  The proposal asks that the Board develop a policy for ensuring congruency between the company's corporate values and its political activity, and report to shareholders on the company's compliance with that policy.

The SEC denied Deere & Co's request for no-action relief in December, and the proposal has been included in the corporate proxy for Wednesday's shareholder meeting.