Pashuteh Yid, Achdus means loving all Jews, NOT becoming kofrim or allowing klal yisroel to become kofrim. Do we say “yeshu is moshiach” to have achdus with Messianic Jews who have unfortunately been taken by missionaries, or do we stick to our beliefs? Do we say achdus with our Conservative and reform brethren and say “toevah marriage is now acceptable” or do we say “We love all Jews, but we do not allow that in our circles”?
Hate the sin, not the sinner. I love all Jews, including apikorsim. I just hate apikorsus.