There are two counter-arguments.
To offer a third, one of the problems with opening up and assuming people will make their own reasonable choices is that not everyone has the financial and social security/stability to make a choice based solely on their risk profile. That is, with stronger lockdowns in place, vulnerable people who would otherwise be exposed to higher risk, say because they need to return to a job that puts them at risk above what they would otherwise be willing to tolerate, are protected.
I feel like your argument (and your later argument about taxing activities) ignores the problem of people below some wealth threshold where they cannot act as they would reasonably like to because their alternative is homelessness, malnourishment, etc., thus they must put themselves at risk to stay alive. That’s very different from the situation of a person who can, say, choose to avoid risky activities without putting their ability to continue to live a life with basic needs met.
The lockdown is a coordination mechanism that protects those without sufficient individual power to choose. Thus, if we want to lift lockdowns, we must acknowledge that doing so specifically disproportionally puts at risk those most protected by the lockdown who otherwise would find it necessary to put themselves at risk to avoid a larger risk.
This is true, but also, we’re not giving people money to keep them afloat while their job is illegal anymore. So having the lockdown might not help that much.
Arguably we should start giving people money again, then lift the lockdowns, to give them the ability to choose.
This is, of course, complicated by the fact that if your old job offers you back your job in-person, you’d presumably be ineligible for unemployment… so we’d have to give people money unconditionally for this to work.
You say vulnerable, low-income people “must put themselves at risk to stay alive”, then propose not letting them do so? A lockdown, by itself, does not give the poor any money. If you wish to prevent them from working risky jobs to support themselves, you must either offer them some other form of support or assert that they have other, better options (“homelessness, malnourishment, etc.”?), but are making the wrong decision by working and thus ought to be prevented from doing so. Being denied options is only protection if one is making the wrong decision.
Do you think these people ought to be homeless and malnourished? If so, that’s a hard case to make morally or practically. If not, you should offer an alternative, rather than simply banning what you yourself state is their only path to avoiding this.
Shelter in place orders create common conditions that force government response to these issues. That the current government is not totally holding up that end of the shelter in place bargain is a problem, and an possible counter to this counter argument.
You’re also exposed to all sorts of risks if you’re “below some wealth threshold where they cannot act as they would reasonably like to because their alternative is homelessness, malnourishment, etc.” even before Corona came around. The situation hasn’t changed all that much.
But, as Elon Musk famously said: “If you don’t make stuff, there is no stuff”.