If he doesn't sign it he literally will be used as a platform by them going into the 2020 election. This is a double edged sword. On one end they set up a situation where they try to limit speech and focus attention on harm to one group of people while calling it a hate speech resolution. If he signs it he destroys any chance of a future for white Americans. On the flip side if he doesn't sign it they use it as a rallying cry going into 2020 that this "confirms" he is racist and that will be their entire narrative.
The mere fact that nobody is standing up to this now to bring that up speaks volumes. This is a set up to either harm the country or harm Trump thus harming the country.