Wasps number eight Dallaglio last week revealed he was not expecting to add to his 85 caps despite remaining committed to doing so.
The 35-year-old upset the Rugby Football Union by criticising England's coaching set-up in his recent autobiography.
But Ashton, who this week was retained as head coach on a rolling contract, said in the Sunday Mirror: "I never have been and never will be a vindictive man.
"If I think a player is the best in that position, or the best servant for England in that position, then he will get selected - it is that simple.
"You cannot operate selection by saying, 'I am not going to pick him or him'. You can't operate like that.
"I didn't like the criticism but, to be honest, it just washed over me. It didn't affect me at all.
"So my message to everyone is that the door is open unless you have retired from international rugby."