1. do not practice with any realism because they believe their art to be too dangerous if practiced with real commitment. Therefore, how can they know that Aikido is effective?
My guess is this is because of differences in training methodolgy. Judo uses randori and shiai a great deal. A fair generalization can be made that many aikidoists do not train with uncooperative opponents at the same level of resistance that judo players commonly use in randori, much less shiai.
At least, that's my guess.