The people advocating that might be confusing analysis with politics. It's annoying when someone criticises your political idea but offers no alternative; it feels (sometimes accurately) that they're disrupting the conversation but offering no input. So in a political debate, a ground rule might be "don't criticise my solution if you don't have a solution of your own".

Rationally, however, that doesn't excuse not assessing the solution. And it's also important to remember that one potential solution is "do nothing" or "carry on doing what we were doing already". So, in most cases, ANY new solution had an alternative solution to which it can be compared.