Are there essentially 2 options?
1. you try and cut the virus off. Lockdown the nation, and deal with the fallout which will include severe effects on the economy. Business failure or just a slow down equals less money for the government to spend on the NHS. You also have the issue of supporting business. What if they are going bust? Should the government pay to support businesses while they pay people's wages?
At the 'end' of this lockdown phase, will you have eradicated the virus? No. Highly unlikely. That ship has sailed. Global travel won't cease, so even if you could stop the virus in one nation (difficult in itself) was lockdown worth it? Furthermore, indications are that the fatality rate is not nearly as bad as the WHO initially publicised.
2. The other option is you try to manage the situation. Isolated those at most risk, and accept that to some degree this virus is not going to disappear. In essence that is the approach this government seems to be taking, using scientific advice. You could argue about how it should achieve the best management. It is possible that to slow rates of people needing ICU beds, complete lockdown is required for a short time.