Thank you for your thoughtful questions. You are diving right in! I love it.
Regarding your first question, it is illogical to claim that there is no absolute truth other than there are no absolutes. That is a self-contradicting statement. You could claim there is one absolute truth, but, it cannot be that there are no absolutes.
Simply for illustrative purposes say you claimed, there is only one absolute truth; the sky is blue. I could counter and say that you have at least made two absolute claims in your assertion; 1) The sky is blue 2) the sky is blue is the only other absolute truth.
But, that can’t be either, because, your original proposition was that there was only one absolute truth and I just outlined two.
For the second objection, you can start by asking what your friend is trying to do by saying that by claiming that there is truth you are suppressing other’s ideas? It seems as though they are trying to suppress your idea.
Truth is not a means of suppression. It is a means of discerning between falsity and truth. This objection stems from a false equivalency. It equates truth with people. In other words, this is my truth and you are using your truth to suppress my truth, and, therefore, suppress me.
This is not an appropriate equivalency. People are equal, ideas are not. I can say that something is not true while maintaining the validity and value of the person who holds it.
Additionally, I can think of few ideas more oppressive than the idea that there is no purpose in life. Truth exists, therefore, purpose exists. You could ask your friend why they are trying to convince you that life has no purpose. Whatever, they say it demonstrates that purpose exists in their motivations. If purpose exists in something so unimportant why wouldn’t it exists in something as important as life?
The claim that all religions are the same stems from a severely superficial understanding of the religions in question. While this objection tends to come from those claiming superior knowledge, it actually demonstrates a lack of knowledge in the area of comparative religion. I would encourage them to study said religions to see if their claim is true.
If Jesus is who He says He is, then we can trust His Word. Examine the historical reliability of the Gospels and then go from there.
Lastly, the claim that bacteria has been found on Mars is simply false. As of this point there is no evidence of life past or present on Mars. But, this is not to say that God could not have created life on other planets. Click here for another discussion on that topic.
I hope you found these answers helpful! I would love to hear your feedback as well as the thoughts of others!