You are wrong. The virus has a higher chance of mutating if left to spread. By slowing the rate of transmission we also slow down the rate of mutation. I bet we would be seeing far more dangerous variants at this point if all countries would have just kept business as usual and allowed it to spread unhindered.

In the mean time we have developed numerous vaccines and possible treatments, and have only seen a handful of dangerous mutations. The lockdowns certainly seem to be working as intended.