I've not said things shouldn't be investigated. There's a big difference between investigating and taking it further than an investigation just on the say-so of what someone says.

Information or an accusation should lead to an investigation which usually (note usually) leads to further evidence.

When it doesn't lead to further, more concrete evidence, that should be the end of it until something more concrete turns up. That's usually the case with most crimes so why doesn't that apply across the board. What's sauce for the goose should be sauce for the gander?