走极端 is a verb-object separable phrase (离合词) meaning 'to go to extremes' or 'to adopt an extreme stance'. The object 极端 can be separated from the verb by aspect markers or modifiers — you can say 走了极端 ('went to extremes') or 走了一次极端 ('went to extremes once'). It is commonly used to describe opinions, behavior, or strategies that become too radical. Do not treat it as a single inseparable word.