Mercy, by its nature, is inconsistent, and will appear to be unfair on the surface. A sin has been committed; it merits a certain punishment; that punishment is being commuted or eliminated.
Our sin merits eternal damnation. But Jesus has taken on those sins. This is an enormous act of love. It is also profoundly unfair.
In a world where local church officials have the discretion to offer mercy and allow some divorced and remarried Catholics to receive communion, there would necessarily be inconsistencies. Some dioceses will be more lenient than others. Some may favor certain types of cases over others.
Our current media and cultural environment is very good at detecting and trumpeting these types of inconsistencies. Particularly if this those who benefit from the mercy are somehow less superficially sympathetic than those who do not (Imagine if a bishop allows a wealthy male Republican politician to receive, but not a poor woman whose first husband abandoned her...)
Thus far, the Church has not demonstrated skill in defending its positions and decisions in an environment (e.g. defending its right to not provide benefits that are in conflict with its values = a "war on women"). So, it seems likely that the fallen humans charged with implementing this policy will essentially grant a blanket amnesty, or apply some "consistent" but unwise rule for when people can be re-admitted.
This, as the critics point out, would represent a fundamental change to what the Church has always taught about marriage.
So, while I think that mercy brings us closer to Jesus, I don't know if we're equipped to handle it.
Ok, that should do it for putting my cards on the table. Now I'll look at the current conflict.