I am still not at that part where I have to decide about the vallaslin, but personally have mixed feeling to let it go or not.
Many old cultures the tattoos are mark of adulthood and part of a heritage - and this is how I seen with the Dalish.
Also it might be slave marks from the old times, but as the old times gone and the old gods are nowhere ... these elves survived a lot, they are minority and hated, hunted, molested by humans. Those who wear the marks the ones who leave behind every root and survive without having a land of their own, without support, luxury from their own strength. Nomads between lands which ruled by humans, kings and soldiers and they still live. They still survive - if for them - for their spirit the vallaslin part of their life, then it is spiritually and mentally something which brings them together, unite them and their faith.
They might be aggressive with others, afraid to loose what they have, having too few numbers to really stand against an army if they would want to burn them out - for everyone else they are minority, savages. The vallaslin unites them, makes them a family no matter how far they are, how much one forced to leave the clan (thought I find it still bs about too many mages in the Dalish thing) - since I imagine one getting theirs requires sort of maturity and they ritually making it once they are certain which god they want to cherish, essentially a serious celebration.
Remove it - even if the Inquisitor cant live among the Dalish anymore with the mark and the pressure lays on their shoulder, but this is spiritually their heritage. It is something deep, something precious, something which can not be removed just like that.
If you decide to get it removed, you really must love Solas (or be really too damn proud to accept anything about slavery) and the following break up really can crush a lot mentally in the poor girl.
As a player I can imagine the depth this can cause and make, but character-wise the vallaslin removal is asked before I know he will be breaking up with me. So this is really a thought decision to make - I building my character up, so my ingame decisions forming her final character so in a way I am excited to reach that part but other hand afraid of it. I not spoiled to myself to check youtube - but even if I would I have no personal feelings for it up until it is the character I forged during my game.
But back to the topic, character wise the removal of the vallaslin is a very harsh move, and has very strong spiritualism behind it, and its meaning, reasons. A bound an eye cant see but the heart feels and carries along everything.
If your character built on doing everything because she must do, but trying also through this influence support her heritage whenever she can in hope she can help her blood, her Family to maybe win some merits out of this - even if she sees their flaws and the mistakes such isolation carries this decision can be fatal if not having second thoughts about it.
I understand why Solas wants to see you without them, he comes from an age this was sign of slavery and he is everything which is about freedom and free thoughts. But he can not see the Family behind this of the modern times - how the vallasin changed its meaning so in my opinion removing it can hurt a lot more and ruin a lot more then it looks like at first. And def not helps the fact he breaks up right away it is done.
But this is another of those little details I personally dig, because this decision is big, and emotionally strong. This is a moment which can be very important in the inquisitors life and even change her entire personality after this.
But it be again that I overthink small details - but this theory and thinking this deep behind a mind makes this part of the game alive to me. :>