There are two possible arguments here to try, and I have only ever seen people lobbying against this change use the one, less persuasive argument. That argument is what I will call the "incentives" argument: that change in the rule provides bad incentives against doing R&D. This argument goes along the lines of "this will cost jobs for R&D workers" or "this will reduce the competitiveness of the US." The other possible argument (that I have not seen cited) is that "R&D" work can be operational, and that forcing capitalization of R&D expenses is a bad accounting practice. This Twitter thread only argues the former.
The glaring problem with the incentives argument is that it gives up the point that the ability to operationalize R&D work is a subsidy for technology and software companies. This is equivalent to asking for a subsidy at a time when startups can pull $100 million with no product and other technology companies are reaping record profits. That is not a particularly persuasive argument, and it triggers bad emotional reactions from people. If not for the SBIR companies getting absolutely shafted, the responses to this argument I have seen from non-tech people range from "fuck you" to "deal with it."
The accounting argument is boring and sort of technical, but also a lot harder to argue against and doesn't trigger a negative emotional reaction. All of the people making the rules will understand it, and the IRS could even make the clarification on what is and isn't "R&D" on an accounting basis without an act of congress. They have kind of done this, but have not been pushed nearly far enough.