Is shipping harmless or disrespectful?

It depends on how far it is taken.

Disrespectful:

• Persisting even when the idol knows about it + says it makes them uncomfortable
• Making fanfics extremely sexual
• Placing a sexual orientation an idol and forcing others to believe the same
• Shipping minors
• Hating on other members of the group to promote your ship
• Making deep-fakes of idols for porn

Harmless:

• Making cool fanart
• Cute compilations on YouTube
• Your photo editing skills get better
• NOT MAKING IT A PART OF YOUR PERSONALITY!