Corona virus's effect on graduate admissions
You presumably did some research before deciding on where to apply to in the first place. That research is still valid. Any other contact with the institution(s) and faculty add to that basis of judgement. 
You seem to presume that there is one uniquely right answer on your choice, and that getting to that one answer requires attending an open house. Likely, almost any choice could turn out well, or turn out badly, all depending on factors totally divorced from the open house. 
Note that many people accept without having been to an open house. So, the decision can be made without going to one. 
You seem to presume that actions to reduce the spread of the virus are unethical, something that I would hotly contest.