The SPLC tries to stay relevant by serving at the left's vicious, attack dog on any person or group that does not agree with EVERTHING!!! on the left's approved agenda. Today the SPLC is more like a rabid beast.
It has long outlived its purpose. The groups that were genuinely big causes of hate and violence, like the KLan (the American Nazis never did amount to much) are mere shadows of what they were fifty years ago.
By it's current "standards," twenty years ago virtually every pol, left or right, would have been on their "hate" list.