No public policy decision is without tradeoffs. Are lockdowns costly in an economic and human sense? No doubt. They introduced wrenching changes in society.
But those costs must also be weighed against the costs of *not* locking down. The Covid virus kills in a regular and predictable way to the point it can be modeled by scientific projections. The human toll of lockdowns can't be measured but if it doesn't reach 220,000+ dead Americans (and I've seen no indication that it has), then it isn't comparable.
And anyway, we're not talking about "lockdowns" necessarily. That is just one tool in the pandemic-fighting kit and should be a last resort.
Much less costly from a social and economic standpoint are the common-sense tools of face masks, basic social distancing, hand sanitizers, etc etc. These measures can be done at a cost of literally free or for less than $10.
Problem is many of the critics of "lockdowns" also have a problem with those much less-costly interventions, which undermines those critics' credibility greatly.