It can be welding a hot thing to a cold thing, but if you dial in the layer height and print speed, the heat from the hotend is going to partially melt the area

It can be welding a hot thing to a cold thing, but if you dial in the layer height and print speed, the heat from the hotend is going to partially melt the area being printed on, resulting in a solid bond. Maintaining a heated enclosure and print bed makes this easier, and eliminates all (or almost all) the warps, layering gaps, and pockets. Slower, smaller layers means more layers and more time per layer. It then becomes a tradeoff of part strength vs print time. Infill selection and parameters let you dial that in after you get layer bonding and temperature set up. Printing solid transparent filament parts is done this way. Adding a laser would accomplish the same thing, but would still require slower speeds and the enclosure to prevent warping.