Possible ramifications of changing federal law to recognize domestic terrorism as a crime

According to this article, there is a reason why the authorities are reluctant to publicly refer to incidents of domestic terrorism as terrorism in the press.

Apparently, if someone affiliated in some way with a group already identified internationally as a terrorist organization, commits an act of violence, the law clearly recognizes that as terrorism and it can be described & charged as such. But if a lone or unaffiliated person commits a similar act, should the authorities refer to it as terrorism, they run the risk of screwing up the case for the prosecution, because doing so establishes a legal basis for the defense to claim that the prosecution is prejudiced against the defendant. It seems to hinge on the fact that the federal government does not yet have a specific charge of domestic terrorism.

I would like to form an educated opinion on this issue, but I don’t know enough. The article alludes in a general way to possible scenarios wherein changing federal law to recognize domestic terrorism as a crime may have negative consequences. I want to understand this better. What do you guys think?