There’s a lot of discussion about whether the Austin Bomber was a terrorist. Dylann Roof (the Charleston church shooter) was not charged with terrorism.
Language matters because words are how we interact with the world, and with each other. When we agree on certain labels for some things, but not other things, it sends a message about what we value.
But if we are going to have a functional political debate, we need to be able to agree on a term like terrorism. It is an emotionally-loaded word, with connotations of an extra level of villainy to an ordinary crime. Terrorist attacks are destabilizing in a way that murders or road accidents are not, even if they kill fewer people.
Terrorism is the use of violence against civilians, in the pursuit of a political goal. This definition is only really used to cover non-state individuals and groups. When states do it it’s normally called “war crimes” or “genocide.”
It may be tempting to want to label nihilistic white men who go on murder sprees for no reason as terrorists. But this isn’t terrorism. It’s something else. Of course, this doesn’t mean it’s OK, it’s just a different category of violence.