You never say you asked for a critique, however my answer is based on asking.
When you request a critique, you have to be prepared for comments you don't want to hear. They may be positive, negative or useless. The person giving the critique only knows what you put before them, not what is in your heart or what you were thinking about. They are not supposed to know that. If you have to explain your objectives or intentions of the art you created, then you can be very certain you have failed in communicating that with your art.
You also have to accept, that everyone who looks at your art, will be looking at it from a different viewpoint or perspective. For instance, someone who draws cartoony or very stylize art will have different comments about realistic art, then the people who draw realistically.
You asked for a critique, so it is not insincere to thank someone for giving a critique. Whether you think it is valid or not. Someone thought enough of your art, to take the time to comment with the intention of being helpful. And that is what you should recognize and appreciate. It would be very ungrateful for you to say, “Well that’s not what I intended, so what you say means nothing to me.”
When you request a critique, it's only polite to thank the person for the critique, whether you like the crit or not.
Another thing to realize, is that this is not a classroom situation, where you know everyone has been instructed on how to give a critique. In this forum environment, people aren't even the same age or have the same level of maturity or education. So you will get comments from people that don't know the difference between criticism and critique or when to be silent. I don’t know how many times, I’ve seen answers to requests for critiques that say, “Well, you draw better than me.” It’s senseless and doesn’t help the person at all and wastes time. Because where’s there’s one comment like that, there is more to follow.
It also bears pointing out that your title uses the word criticism. So when I started reading the actual text and discovered you were talking about critiques, I was very surprised, because criticism and critiques are not the same thing. Criticism is only finding negative and hurtful things to talk about. Critique is designed to comment on the positive and the negative, While it may still be hurtful to swallow, the intention is to be helpful. A critique also usually includes a solution.
You also mention wanting to have conversations, which is a whole ‘nother animal. A conversation is an exchange of ideas. If that’s what you want, then don’t ask for critique. Clearly say, “Hey, this is what I’m trying to accomplish. Am I successful? If not what do I need to do? If I am, can I make it better? Has anyone done this before? etc. etc.”
I’ve given plenty of portfolio reviews at conventions, as an instructor and as a colleague. Sometimes, I ask before I even look at the art, 'Do you want it hard of soft?' The ones who answer,”Hard” are the ones I respect, because I know they are serious. The other ones are more concerned about their feelings, than their art. The ones who want it hard will also learn more.
At the risk of seeming to pat myself on the back, I want to share this story to make a point. More than once, years later, I’ve had artists come up to me and tell me I gave them a critique, which they thought at the time was very harsh. Later they realized, I was right and told them exactly what they needed to know and then thanked me for giving them that critique.
Put your feelings aside. What you may feel is not helpful now, may change 6 months from now when you think about it.
All critiques you receive are not meant to be used. You have to balance that against what you're trying to achieve. You do that balancing act on your own, not in public. One thing you can be sure of, if you keep hearing the same thing over and over, then that is not just someone's opinion. It is a fact you can't ignore him have to address in your art.
So when you ask for critique, don't defend; don’t explain; don't justify and above all don't whine. Accept all critiques in a graceful, professional manner, which is quietly and with a, “Thank you for taking the time to comment.”