The biggest problem with tag-based languages (<h1><% someCode %></h1> : the ASPs, the ColdFusions, the PHPs...) is that they facilitate monolithic code. This is related the big criticism of XML and DOMs for data structures, too: they facilitate the creation of hierarchies, not graphs. (As always with programming, the issue is "facilitates" not "possible"...)

My dear friend "Bob" creates horrific pages that are hundreds and even thousands of lines long, with <cfif> at line 100, and then a <cfelse> at line 837 and then a ... and ColdFusion isn't valid XML and there's a combination of HTML indentation and ColdFusion code indenting.

Just absolutely impenetrable stuff, and while I'm more than willing to blame many problems on Bob, I think this is a problem that the tool he uses (ColdFusion) is facilitating.