Sometimes, people actively discourage you from your goals and dreams. It is possible they care and are worried. Maybe they are jealous and mean-spirited. There are responses to a verbal takedown of your aspirations, but there is nothing you can say to a disapproving silence.
You can try, of course. Feel free! You'll only be rewarded with a variation on the reply, "I didn't say anything."
Silence can be incredibly powerful. When disapproving, it implies an idea or aspiration is so awful that words are unnecessary, or that the speaker's stated goal is evidence of such profound idiocy, any attempt at 'helping' the offender would be without purpose.
This form of silence can only imply these thoughts, because it is disapproval based on confusion, anger and sometimes willful ignorance. The gay man who mentions his spouse to a suddenly inert listener. The musical kid who shares her passion to silent, frowning parents. The friend who writes of his good fortune from his new city, while the bff he left behind simply scowls. The author who shares her stories with loved ones, who declare them garbage to others but say nothing to the author herself.
We tell ourselves and those we love that criticism can be helpful, but no constructive feedback can be parsed from silent disdain. If you respect, cherish, and believe in a friend or family member who shares with you their aspirations, give them your polite but honest feedback. If you have nothing positive to say, and the goal isn't evil*, your reply can simply be, "I don't understand this, but I'm glad you are happy."
If you are the silence-recipient in this scenario, stop sharing your interests with that person and consider whether a relationship is salvageable. Usually it isn't. If you are the one dishing blank contempt in response to a person's interests, you're a shitty friend.
*I've had people share some seriously messed up ideas with me, where my stunned silence could be misinterpreted as what I describe above. Evil goals are excluded from my argument.