I am an ex-vegan and I never considered myself a "failed" vegan, I just saw my opinions and values changed over time. Personally, I think my perception changed and that my morals regarding animals had nuances that I shut down internally because I thought that those opinions made me a terrible, bad person with subpar discipline.

While I have the experience of a vegan and subsequent ex-vegan, I would never lash out at other vegans, because I remember my opinions and passions. If anyone does that to you and disrespectfully warns you, you have every right to be upset. It makes sense for them to relate to you and share their own experiences - but only in a respectful way. Those conversations are extremely difficult because they could easily turn into a hurtful conversation that seems like they are dismissive and intent on sabotaging your beliefs. Ultimately, it's up to you if you think that that exchange should be warranted or not.

I'm sorry that your friends are giving you such attitude - they should be supporting you and respecting your values, instead of lashing out due to their own sense of failure. In many situations, we project our experiences onto other people - like these ex-vegan "apostates".

I know personally, that I react similarly to some of the comments in this thread, like "You obviously don't care about animals.", "How could you possibly shift to the other side after this?" I wouldn't want to hear those comments unless I engaged the conversation. I think for your friends, they should keep it to themselves unless asked - and you should politely express that their opinions are patronizing, harmful and you don't want to hear them. They had their experience, now they should allow you to have yours, and treat you like an adult who has considered all aspects of veganism before you subscribed.

I obviously still carry over conscious habits from my vegan days, which is why I'm on this sub. I'd have this conversation with them, and when they understand and respectfully approach the topic (if you want) - I think a nice conversation middle-ground would be things like "Are there any habits you carried over? Favorite vegan product?" that are light-hearted and celebrate their positive past experiences.