I would think of this as generalized aversion.
Aversion is a hindrance, one if the five hindrances. Whenever one notices a hindrance one should direct the mind accordingly.
If thinking about doing a certain contemplation seems tedious then one should resolve that aversion before doing anything else. One does this by recognizing the circumstances, properly reflecting and secluding oneself from the triggers mentally & physically. When a stilling of unwholesome thoughts has occured one can just enjoy that and not worry about whether one used metta or whatnot to attain it.
There is nothing repulsive about metta contemplation but contemplation or meditation in general can become repetitive & a chore. It is especially boring if one is putting in a lot of work but get's neither special rapture nor lights & visions.
How one deals with aversion is a matter of trial & investigation. One should learn many skillful means such as redirecting the mind to the body and the themes of appriciation & etc. One might think that metta counters aversion but if one is averse to doing it, as one has been doing it, then it isn't at that time suitable and one can choose to investigate the aversion or choose another gladdening theme such as ie compassion, appreciation, equanimity, virtue, The Buddha and whatnot. One can also do breath work to shut out distracting thoughts and thus create distance & attain seclusion in order to perceive the grand distinctions such as lights & visions.
Forcing oneself to meditate with an aversive mind is not a good idea but the stilling of aversion is a meditation and a good idea.
You can also try mixing things up to avoid monotony in contemplation, try different ways of rousing the mind and develop wholesome themes by giving of attention as you see fit.