Is it obligatory to despise the innovator and outwardly show him enmity when warning against him, and is there any further detail regarding this?

Circumambulating graves is polytheism (shirk) because circumambulation is an act of worship to Allah, and directing an act of worship to other than Allah is polytheism. Those who circumambulate graves must be advised and informed that the interred person possesses neither benefit nor harm, and that benefit and harm are in the hand of Allah alone.