Leaving aside the probably wrong price (PeeD claims the Karrar would cost as little as $500,000), I don't know if I've said it before but I don't care what they're mounted on, ATGMs will not replace tanks.
ATGMs use HEAT warheads which are less effective against tank armour (especially ERA), and they are also slow moving which makes them vulnerable to APS. But the most important thing is that ATGMs are strictly defensive weapons. They're carried and fired by squishy humans or lightly armoured vehicles (no tanks, remember). Said vehicles usually have to sit still to guide the missiles, unless they're using expensive fire and forget missiles like the Javelin. ATGMs are also quite limited in their use. Of course, they can be used to destroy infantry and structures, but not cost-effectively.
Tanks on the other hand, are highly mobile, can fire on the move, and are heavily armoured. They can actually conduct offensive operations. You can say Iran doesn't want to invade anybody, but if anyone invades Iran, we want to have the initiative and be able to launch counteroffensives.
They also have versatile firepower which enables them to engage all sorts of armour, infantry and fortifications in an effective way. APFSDS, HEAT, and HE rounds, along with heavy and/or medium machine guns all have their own job.
